It turns out that several important modelling addons depend on the assumption
that Grease Pencil data gets created on the active object instead of on scene
level. This commit adds a toggle for setting whether new Grease Pencil data
is created on scene or object level.
These work as follows:
* "Scene" = The behaviour originally introduced as part of the GPencil_EditStrokes
changes. New strokes are added to the scene instead of the active object, making
it easier to manage things when working with Grease Pencil in general.
* "Object" = The previous behaviour (from 2.50 to 2.72), where new strokes are added
to the active object. This is now being reintroduced to soften the transition
for addons out there which have been doing this in a lazy/lax way so far.
Now, what may be slightly confusing are the "fallback" measures in place:
* "Scene" - To ensure that loading old files goes ok without needing a version patch,
if the active object has GPencil data, that will be used in place of the scene's
own GPencil data.
* "Object" - If there was no active object at the time of creating strokes
(for instance, if you delete the active object immediately before drawing),
GPencil data gets attached to the current scene instead.
Since some tweaks may still be needed here, I've decided to bump the subversion
number so that we have a reference point when doing version patches.
fe4d0c234e