Blender Git Loki

UI: Tweak Sequencer Sidebar panels

Even though we are in UI freeze, we agreed that this should be better, and so we are changing a few things:

- Clearer separation of controls that affect the image transform vs the video
- New Transform panel houses Flip X/Y, Offset and Crop
- Flip X/Y now uses toggle buttons like we do for mirroring elsewhere (clearer + takes up less space)
- Video panel only includes things that relate to playback, ie Playback Direction, Strobe etc.
- Backwards/Forwards playback is now an enum rather than a toggle (we should always use enums when it's not an on/off switch)
- Rename Input panel to Source
- Just more immediately understandable and correct
- Move Deinterlace here since it's source file dependent
- Move Source panel to be a top level panel
- Merge Info and Timecodes panels
- Move Lock toggle to Info panel (was previously attached to name field which made no sense whatsoever)
- Name field now uses full width and doesn't add redundant text in front of it
- Re-arrange tabs to be Strip, Modifiers, Proxy & Cache, View
- Strip and Modifiers should be together

Reviewers: brecht, iss

Differential Revision: https://developer.blender.org/D5098