Convert user navigation to a dropdown menu

This pull request replaces the user, "home", "inbox", and "logout" links with a compact dropdown menu.

![image](https://f.cloud.github.com/assets/98601/972828/31057b18-060a-11e3-8a4b-1dddace1ad90.png) ![image](https://f.cloud.github.com/assets/98601/972825/163a8990-060a-11e3-94dd-ad83843b1043.png)

The menu has the following advantages:

* Looks better than a generic list of blue links
* Provides a more verbose explanation on the "Go to Home Location" action
* Provides direct links to user sub-pages without taking up space in top bar
* Gains horizontal space, making it more feasible to switch to a single line header on narrows screens -- something like ![image](https://f.cloud.github.com/assets/98601/964986/f5a8e82c-0521-11e3-90bc-79324cacd2d5.png) rather than ![image](https://f.cloud.github.com/assets/98601/965029/99463ffc-0522-11e3-8f24-fb7509f550ca.png).

I also converted the edit menu to the same style:

![image](https://f.cloud.github.com/assets/98601/965009/3e848204-0522-11e3-9da8-cc416610c1b4.png)

And instead of a popup alert, the minimum zoom constraint is now exposed in a tooltip:

![image](https://f.cloud.github.com/assets/98601/965016/557a3602-0522-11e3-9eed-cdbdca3e1cb7.png)