CSV animation file format export-import plugin for Krita

This plugin can export and import TVPaint's layered animation
format. The format contains a CSV (comma separated values)
textfile (filename.csv) and a directory (filename.frames)
with png images of the keyframes. TVPaint itself can only
export this format, but I'm working on an importer script
for TVPaint too.

Differential revision: https://phabricator.kde.org/D1068