content template improvements

This pull request applies some changes to the content templates for better usability. **Please do not merge this pull request yet since further commits regarding the content form template are planed.**

Content List
----------------
![unknown-1](https://cloud.githubusercontent.com/assets/2105496/3934495/f25c7a14-248b-11e4-9792-89c57f85cca3.png)
I replaced the breadcrumb navigation by a filter form. That way, administrators can easily navigate between the contents of different pages while it remains the clarification to which page the currently visible content is assigned to.