Somewhat intermediate checkin with a lot of changes and some preliminary
structures in place for further extension of tack functionality.

1. Tacks can now be SoundCloud elements
2. Youtube (yiitube) elements are now sized properly

TODO:
1. Make tack board bigger for tacks (est. 20 minutes)
2. Fully implement Marketing's tack templates (est. 3o mintues)
3. Make boards act like tacks (est. 1 hour)
4. Allow search/browse (est. 2 hours)
5. Generate tacks on homepage (est. 1 hour)
6. Change background to Marketing's decision (est. 30 minutes)