Blender Git Loki

Dopesheet-Timeline: Somewhat hacky version-patching code to switch old timelines to dopesheet-timelines

After a lot of failed attempts and head banging working trying to find a way to reuse
the standard editor-switching/creation code, I've just hacked in a temporary solution
here so that users can load old files and see the old timeline instances replaced
with Dopesheet-Timelines.

Note: This is not nice code, and copies a lot of the standard initialisation code,
but it works well enough for now. We can revisit this later when the other mode changes
come along.