ENH: MovieStim2 and demo

MovieStim2 should now work in terms of all public methods and input args
I think.

Looping is also working now.

Demo shows how to use start, stop, pause, seek, and volume up and down.

Jeremy, I tried 3 videos when running demo script within PsychoPy Coder,
and all seemed to work fine. Please let me know if u see issues.

Not 100% happy with audio / video syncing all the time (it is not always
within 1 frame synced), but seems usable from the 10 videos have have
tried. Time could be spent improving it more I think, but I am out of
time for this. ;)

One video I have is corrupt because of no key frames (as informed by
text put to stderr from openCV). It plays, but pausing or seeking makes
it all messed up. Playing the video using VLC also shows issue; video
play position can not be changed with slider gui; and instead the movie
restarts each time slider is moved by user. So I think this is a genuine
video file issue.
Delete old movie2 demo