Added limited support for simulation caches on override data-blocks
(caches need to be written on disk for now,
59910f72,
7e210e68,
50ccf346).
Added initial support for NLA on override data-blocks (one can add new
tracks to existing NLA system, and edit some properties of the
existing tracks and strips
(c0bd240ad0).
Some heavy data from override IDs do not get written to disk in the
local .blend file anymore (mainly mesh geometry, shapekeys data, and
embedded files currently, see
D9810,
f5a019ed43).