package daemon: Rework error and issue propagation to client

* BDaemonClient: Move inner class BCommitTransactionResult to top level
and make it public.
* BCommitTransactionResult:
- Add a whole bunch of specific error code enum values. Such an error
code is now the primary error, as opposed to before where we would
mix status_t and enum value errors. There's a systemError property
of type status_t which may provide additional information, though
(depending on the primary error type).
- Remove the errorMessage property. Due to mapping all errors to the
specific error codes this is no longer necessary. Mixing such a
message with another error description is also not very helpful when
it comes to localization (still not supported, though).
- Add several properties (paths, strings, error codes) that serve as
arguments to the primary error and are used by FullErrorMessage().
- Add issues property, a list of instances of new class
BTransactionIssue. Those describe non-critical issues (e.g. failed
update of a settings file) that occurred in the process of
committing the transaction. Those issues should be presented to the
user by the package management program.
* Exception: Adjust to transport the BCommitTransactionResult
properties.
* CommitTransactionHandler, FsTransactions, Root, Volume: Adjust to
BCommitTransactionResult/Exception changes.
* CommitTransactionHandler: Now requires a BCommitTransactionResult to
which it adds the issues it encounters. The reply BMessage is no
longer needed, though.
* Volume: Refactor common code from the three methods that use
CommitTransactionHandler into new method _CommitTransaction.

package daemon: Implement writable files handling

* Move Volume::Exception to top level and into own files.
* Add utility class FSUtils, move Volume::RelativePath there and add a
bunch of FS utility functionality.
* Add FSTransaction, a helper class to record FS operations and revert
them.
* When activating a package we now extract the writable
files/directories it declares. The handling is not quite complete:
- We don't handle merges yet. I.e. the user will have to do that
manually for now.
- We don't propagate issues/infos regarding the writable files (e.g.
that a manual intervention is required) to the user yet.

package daemon: Rework error and issue propagation to client

* BDaemonClient: Move inner class BCommitTransactionResult to top level
and make it public.
* BCommitTransactionResult:
- Add a whole bunch of specific error code enum values. Such an error
code is now the primary error, as opposed to before where we would
mix status_t and enum value errors. There's a systemError property
of type status_t which may provide additional information, though
(depending on the primary error type).
- Remove the errorMessage property. Due to mapping all errors to the
specific error codes this is no longer necessary. Mixing such a
message with another error description is also not very helpful when
it comes to localization (still not supported, though).
- Add several properties (paths, strings, error codes) that serve as
arguments to the primary error and are used by FullErrorMessage().
- Add issues property, a list of instances of new class
BTransactionIssue. Those describe non-critical issues (e.g. failed
update of a settings file) that occurred in the process of
committing the transaction. Those issues should be presented to the
user by the package management program.
* Exception: Adjust to transport the BCommitTransactionResult
properties.
* CommitTransactionHandler, FsTransactions, Root, Volume: Adjust to
BCommitTransactionResult/Exception changes.
* CommitTransactionHandler: Now requires a BCommitTransactionResult to
which it adds the issues it encounters. The reply BMessage is no
longer needed, though.
* Volume: Refactor common code from the three methods that use
CommitTransactionHandler into new method _CommitTransaction.

package daemon: Implement writable files handling

* Move Volume::Exception to top level and into own files.
* Add utility class FSUtils, move Volume::RelativePath there and add a
bunch of FS utility functionality.
* Add FSTransaction, a helper class to record FS operations and revert
them.
* When activating a package we now extract the writable
files/directories it declares. The handling is not quite complete:
- We don't handle merges yet. I.e. the user will have to do that
manually for now.
- We don't propagate issues/infos regarding the writable files (e.g.
that a manual intervention is required) to the user yet.