Improve theme discovery
The gh-pages should help users find themes by allowing them to filter themes by template lang/preprocessor support(jade/less) and theme purpose (blogging/docs). 

Users should be able to see screenshots of the filtered themes as mentioned in https://github.com/colinwren/Cabin/issues/3 and copy a shell command that they can then run to scaffold out their project.

Example: If the user filtered by Sass and EJS there is no need to prompt them about preprocessor or template language and we can just use  `--Sass` and `--EJS` options.

```
cabin new blog colinwren/Blok --Sass --EJS
```
