Blender Git Loki

Annotations: WIP first steps towards toolbar support

This adds a toolbar entry for activating the annotations tools
as active tools. Many things are WIP still (e.g. tool settings
are yet to come, as the necessary props aren't defined in DNA/RNA yet).

Todo's:
* Icons are missing. The necessary icons *do* exist right now
in the icon_geom.blend file, but I can't get them to export/generate
.dat files that we can use in the UI here. That said, the placeholder
names (from that file) are now used.

* Key mappings need work/testing. They seem to work well enough as-is
already though

* Tool settings (in topbar) are not implemented yet. Coming soon
(aka tomorrow, after I get some sleep)

* Non-3D view toolbar support