Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

setup.py: depend on 'pyyaml', not 'pyaml'

In the pip namespace, 'pyaml' is "pretty-yaml", a YAML generator (but
not a YAML parser); 'pyyaml' (accessed with "import yaml"), a.k.a.
"PyYAML", is the YAML serialiser and reader we actually use.

Bump the minor version number per semantic versioning rules. (One could
argue that we are "removing" pyaml (pretty-yaml) from our interface and
therefore a major version bump is required, but we weren't _actually_
using that module so I would argue that the introduction of 'pyyaml' is
the visible change.)

Thanks to Japheth Lim for identifying this issue.

setup.py: add Python dependency on libarchive-c

The `shoehorn` tool in tools/seL4 (the sel4_tools repository) requires
this.

Bump minor version number per semantic versioning rules (interface
extension). (0.3.1 instead of 0.3.0 because 0.3.0 saw the light of day
with an incorrect dependency on `libarchive` instead of `libarchive-c`.)

Revert "setup.py: add Python dep[] on libarchive"

This reverts commit a14264336c9e10328236c06fdd3b5197a3cc7698.

There are (at least) 3 namespaces relevant to Python module names:
Debian package names, PyPI module names, and the name of a module used
by actual Python language imports. That's one more than my brain could
handle. I wanted "libarchive-c" in setup.py instead of "libarchive".

setup.py: add Python dependency on libarchive

The `shoehorn` tool in the tools/seL4 (the sel4_tools repository) will
require this in a future commit.

Bump minor version number per semantic versioning rules (interface
extension).

trivial: add trailing comma to list element

Python syntax allows a comma after the last element of a list, and
having one helps avoid surprises in the event the lines of the list
are rearranged.

setup: add versioned dependency on pyaml

In commit 24131333acdb38ab0f9a2d35beec4930739f808b ("trivial: disable
YAML loading warning"), an assumption was made that the version of pyaml
present was 5.1 or later; see https://msg.pyyaml.org/load .

Version the dependency.

python2 --> python3

Update all scripts and build system to call python3, given python2's
upcoming doom. Use sys.maxsize instead of sys.maxint in one script
(maxint does not exist in python3).

python-deps: Add pyelftools to sel4-deps package

This dep is required by the elfloader for loading Arm and RISC-V
platforms.

python,sel4-deps: Pin versions for style tools

These tools sometimes style differently across different versions.

tools: add autopep8 dependency

tools: add guardonce python dependency

Fix cmake-format dep name

python-deps: add cmake-style

Update pydeps version

This is due to the new dependency, pyfdt

python deps: add pyfdt

python deps: add jsonschema

This will be used to validate the kernel's hardware configuration file
against a schema.

python deps: add seL4 tutorial deps

Update sel4-deps for tempite->jinja2

tools: fix licenses

python-deps: add bs4

Add pip metapackage for downloading dependencies

Dependencies can now be downloaded with:
pip install sel4-deps

Dependencies can be changed by modifying the setup.py script.

Information on how to update the package is in the setup.py script.

JIRA: SELFOUR-909