Blender Git Loki

Annotations: First steps towards having working annotations again

Copy-back (from 2.8) and split out "Annotations" drawing operator/rendering
code from the "GP Object" versions of the same code.

Notes:
* All "annotation" related things are now in the annotate_*.c files,
while "drawgpencil.c" and "gpencil_paint.c" are for the GP Object only
now. This will simplify maintenance of the two different usecases,
as the GP Object versions are significantly more complicated and filled
with extra cruft.

* The general "Grease Pencil" keymap (i.e. the one that allows DKEY+LMB-drag
to draw) is now for annotation usage only. For GP Objects, you can add a
blank GP Object, enter Draw Mode, and start drawing.

Code Changes:
* Removed all 2D drawing-code entrypoints from drawgpencil.c

* Cleaned up most of the annotate_paint.c and annotate_draw.c code
to remove stuff that annotations won't use (e.g. brushes, palettes,
fancy line effects, etc.) As much as possible, these have been restored
back to a pre 2.77 state - with the notable exception of per-layer
Onion Skinning, for which the settings were removed already.