Blender Git Loki

Clip editor: cleanup up header

One side of change is related on making code easier to follow, due it started
being quite messy because of all in-lined mode/view checks. Now there's a bit
of code duplication, but it's much easier to see what's going on there.

Another side of patch is related on re-arranging elements in header in a way
that follows rule "depending elements are placed after elements they depends on".
This might be a bit against mostly-used-based elements placement, but now it's
much easier to figure out where to add new option. Also it fits better other
blender's areas such as image editor header, i.e.