Blender Git Loki

Replace old Timelines and Logic Editors with new Dopesheet (Timeline mode)

Timelines and Logic Editors are gone. So far they were simply replaced by broken
Info Editors, now they are replaced by Dopesheets in the new Timeline mode.

We reuse ScrArea.butspacetype to temporarily store the space-type identifier of
the deprecated editor (see 9db492de6dd07). That way we can identify it in
versioning code and replace it nicely.
Action editor creation needs a scene to set the scrolling based on frame range.
Active screen-layouts use the active scene of the window they are displayed in.
Inactive screens simply use the first scene in the main data base.
Note that inactive editors don't need version patching, readfile.c converts them
to SPACE_EMPTY already, so users can't activate them.

Files saved since the editors were removed will still be broken.
Workspace config files saved before this will also crash (will update default
one in followup commit).