Video player support

Using the api for HTML5 video to get the currentTime property. Works
for basically all web video. Also incorporated updating the note on
ctrl-return for getting the new time stamp. Works great but means that
clearing the field doesn’t work.
TODO: somehow clear the selection…
Also, YouTube has a strange bug where once you make a selection, that’s
all you get until you make another explicit one… odd.
Code cleanup

Cleaned up the content script to help reduce loading time.