Tag information now displays min:sec

Fixed the showing of pixel location instead of time in video. Now
displays min:sec. Added helper functions for this.
calcTime takes a pixel value and converts it to seconds.
convertTime takes seconds and converts it to a string with min:sec
Added link in Tweet text (unfinished)

Now only displays the current link with ?time=0.
More required:
- Having the time live. See
http://stackoverflow.com/questions/10486354/dynamically-change-tweet-button-data-text-contents
for a solution.
- Error checking when a ? is already present in the link, so as to not
add another one.
Merge branch 'master' of https://github.com/wrvangeest/Context

Conflicts:
	Prototype3/javascript/tagdata.js