speed up concat by moving, not copying the video file

[kieranjol]

Currently concat.py makes a single MKV in the output directory, then copyit.py's it into the objects directory. This takes a lot longer than it needs to but it's handy as it's less code to write.
A work around that makes a lot more sense is:

• move (not copy) the file into objects
• manifest.py -s to create a sidecar manifest

This should create the same files as the copyit process and the rest of the script should run as normal.