Blender Git Loki

Load image sequence collapsing for sequencer

Very dirty feature that will have to be reimplemented when the new asset engine makes it into blender.

This commit tweaks the filebrowser to detect sequences of images that form parts of a movie. The
files need to be in the format <number>filelame.ext or <number>.filename.ext

There is a new option next to hidden file option that makes it so this collapsing takes place.

When collapsing is on, any movie files that have the same filename will be collapsed to the first
detected file in the sequence. Selecting that file will select all files in the sequence.

There is a shortcut in the sequence editor in the Add menu, "Image Sequence" that enables collapsing
by default. Unfortunately, selecting multiple movies will not add multiple sequences to the sequencer,
at least for now, but it should make it quite easier for people to quickly select the whole range of
images for a movie. Importing the image sequence into the sequencer will use placeholders, so any missing images
will display as black.