This fixes:
* free_imbuf_seq() didn't free all scenes. That will lead to steady memory
growth in case of nested timelines with several scenes.
* sequencer panels were always jumping around, depending on strip type,
which was caused by choosing always the same panel position and the
silly limitation, that
* effect strips had no filter option, which was therefore added.
So you can apply color balance on effect filter output now :)
36e96e5b6e