Integrate in BIIGLE about videos

[mzur]

This is now a BIIGLE module instead of a standalone application. It adds the videos, video_annotations and video_annotation_labels database tables. In principle a video annotation also could be stored in the old annotations table, but:

• The annotations table has the image_id foreign key of the images table.
• Video annotation points and frames would need to be stored in the single points column.

I decided to create a new table for video annotations because this is a cleaner solution with the video_id foreign key and separate columns for points and frames. Also it's much easier to distinguish between still image and video annotations. We only need a separate count for video annotations in the admin dashboard.