Theme tweaks.

Made light theme Brackets' default theme and tweaked dark theme so that it's basically the light theme with a dark background with additional color changes.

![screen shot 2014-06-08 at 10 34 13 am](https://cloud.githubusercontent.com/assets/1495261/3211848/4e207410-ef33-11e3-9066-f8dae6736cb4.png)

![screen shot 2014-06-08 at 10 35 24 am](https://cloud.githubusercontent.com/assets/1495261/3211850/550a8af4-ef33-11e3-8c4f-30ab7b9af047.png)