Blender Git Loki

GPencil - Added operator to copy selected strokes

Code cleanups

Replaced inline GP stroke-looping logic with macro-based iterators

These are quite rough, and we may yet just dump this info in Context instead
using the standard techniques...

GP Circle Select

It's now possible to use Circle/Brush Select (D+C) to select individual Grease Pencil
strokes. This will eventually be useful for editing operations using these.

Implementation Notes:
* This is currently a quick and dirty implementation, which just copies and pastes
some of the logic from the eraser, and reuses some of the same utility functions
too.
* The shared methods are now exposed internally for use in the gpencil module.
Perhaps they should eventually get their own dedicated section/file?

GPencil Strokes: Select All Operator

Added a "Select All" operator for Grease Pencil strokes which will
select all strokes on visible layers.

Usage:
* <D> A = Select All (i.e. hold down D and press A)
* <D> Ctrl I = Invert All (NOTE: this one may be removed, as it's quite awkward)

Added a "select" property to GPencil strokes

This property doesn't serve much purpose yet, but will soon be used to tag strokes
for modification by "in-viewport" stroke editing tools.

As a temporary visualisation hack, this uses the abandoned "debug" drawing mode
code, which plots out all the points of the stroke. We might want to replace this
with something nicer later, but this will do for now.