IA Pages Index - make the whole sidebar fixed

Hello, sticky sidebar!
I have also made some modifications on topics and templates filter sections to make them look more like actual dropdowns:
![screen shot 2014-12-05 at 16 11 42](https://cloud.githubusercontent.com/assets/3652195/5490394/729e1014-86d1-11e4-8841-5b77642f5a31.png)

@russellholt @jagtalon