Improve custom theme functionality - updating sub themes.

#4948
![appearance 2 john](https://f.cloud.github.com/assets/1222368/2009258/713eafc4-875b-11e3-9022-39d344a39d7d.png)
![appearance john](https://f.cloud.github.com/assets/1222368/2009257/713d200a-875b-11e3-99c0-586700cc35aa.png)