Blender Git Loki

Tests: Blendfile-loading test class

This new test class minimally sets up Blender so that it can load blend
files and construct a depsgraph without crashing.

Note that it hasn't been tested on very complex blend files, so it may
still crash when the loaded blend file references/requires uninitialised
data structures.

The test will certainly crash with Blend files created with Blender
older than 2.80, as the versioning code requires space types to be
registered. This is normally done by initialising the window manager,
which is not done in this test. The WM requires Python to run, which in
turn requires that Blender finds the release directory in the same
directory that contains the running executable, which is not the case
for GTest tests (they are written to `bin/tests/executablename`.

Reviewed By: sergey, mont29

Differential Revision: https://developer.blender.org/D6246