MediaAddOn: missing const

Pretty much all add-ons are setting this to point to a const string, so
we should make sure that nothing tries to modify it.

vst_host: use FindPaths instead find_directory

vst_host: remove vstplugin folder creation, code clean-up

Remove B_COMMON*_DIRECTORY and kCommon*Directory constants

* This does intentionally break source compatibility, so that a review
of concerned code is forced.
* Binary compatibility should be maintained in most cases. The values
of the constants for the writable directories are now used for the
writable system directories. The values for the non-writable
directories are mapped to "/boot/system/data/empty/...", an empty or
non-existent directory, so that they will simply be skipped in search
paths. Only code that explicitly expects to find something in a
B_COMMON_* directory, will fail.

Style cleanup: removed unnecessary braces.

Style cleanup. 80 character line limit.

Added VSTHost media add-on.

vst_host: use FindPaths instead find_directory

vst_host: remove vstplugin folder creation, code clean-up

Remove B_COMMON*_DIRECTORY and kCommon*Directory constants

* This does intentionally break source compatibility, so that a review
of concerned code is forced.
* Binary compatibility should be maintained in most cases. The values
of the constants for the writable directories are now used for the
writable system directories. The values for the non-writable
directories are mapped to "/boot/system/data/empty/...", an empty or
non-existent directory, so that they will simply be skipped in search
paths. Only code that explicitly expects to find something in a
B_COMMON_* directory, will fail.

Style cleanup: removed unnecessary braces.

Style cleanup. 80 character line limit.

Added VSTHost media add-on.