Updated to match new white mockup

Finished up the rework:

![screen shot 2014-11-17 at 7 56 30 pm](https://cloud.githubusercontent.com/assets/6354033/5082363/06eaab3e-6e94-11e4-99fa-4bd48573fb7a.png)

There are two functional changes:

Clicking on the header should reveal the sub-menu's contents.

![screen shot 2014-11-17 at 8 06 50 pm](https://cloud.githubusercontent.com/assets/6354033/5082446/54913e2e-6e95-11e4-9eaf-0c04af505faa.png)

![screen shot 2014-11-17 at 8 06 58 pm](https://cloud.githubusercontent.com/assets/6354033/5082449/56b8f7c8-6e95-11e4-9195-b86a0e9ce84b.png)

An overlay on top of the timeline should always leave one row more than what's been used so far. That is, if only the top three rows have blocks in them, the user should only be able to add blocks to the top four rows. If there are no rows in use (no blocks on the timeline), then the user should only be able to add blocks to the top row.

![screen shot 2014-11-17 at 8 08 23 pm](https://cloud.githubusercontent.com/assets/6354033/5082470/99172482-6e95-11e4-877b-fbc33c523c64.png)

![screen shot 2014-11-17 at 8 08 35 pm](https://cloud.githubusercontent.com/assets/6354033/5082466/946766e0-6e95-11e4-9907-d486a0af5b80.png)
Reset `RECTANGLE_WIDTH` here in case it's created and set before `timeline.js` gets loaded. Let me know if you think it's better that I just replace `RECTANGLE_WIDTH` in `events.js` with the hour width constant.