Improve font rendering and management

@devoncarew

1. Turn on non-subpixel antialiasing for fonts: makes fonts crisper and much better looking, especially on OSX and especially light ones on dark backgrounds. This is also a global trend for Google properties.
2. Replace scattered font-family setting with just 2 central locations (1 for the widgets and 1 for the app) - will make it easy to quickly switch fonts if necessary.
3. Add Helvetica Neue as the top preferred font.

BEFORE:
![screen shot 2014-05-24 at 12 30 17 am](https://cloud.githubusercontent.com/assets/5606182/3073922/1cc3940c-e316-11e3-88a1-9a69deeaf4ce.png)

AFTER:
![screen shot 2014-05-24 at 12 28 40 am](https://cloud.githubusercontent.com/assets/5606182/3073928/8c677f44-e316-11e3-9176-8d23d99d45fb.png)