Filenames of Animation-Frames: add more informative types of place-holders

[mafrieger]

would be very handy to have some more options on names of frames output images in form of additional informative place-holders
to number
1)  consecutively (frame number)
2) with time-stamp
3) progress in percent of total animation
4) with some content information from timeline
e.g. names of all active lines in combination with one of the above
"great-animation_134_door-moving_light-glowing.jpg"

This is especially helpful when working on detailed documentation of animations and looking for special frames
e.g.
- for preparation of
-- cutting
-- sound recording
- generating some kind of Preview
- for general documentation on customer request
- ...