Support for minimalist themes

This kind of breaks the yin-yang dichotomy, but I did this for fun and was quite pleased with the result so I thought I would share. Basically it adds supports for new themes besides the two original ones. With this commit:

- solarized light
- solarized dark
- autumn
- dracula
- typewriter
- friends of symfony


To add a new theme all that needs to be done is duplicate any of the folders under "themes/", change its name and make the desired modifications and then add the theme name (same as the folder) in this array:

var themes = ['original-yin', 'original-yang', 'solarized-light', 'solarized-dark', 'typewriter', 'autumn', 'dracula', 'friends-of-symfony'];

Currently located in js/ui.js at line 145

If anything fails, the automatic fallback is the original yin theme, since nothing is changed in the original css