Added "recent_posts" function, fixed some CSS, more Cascade routes, fixes for Admin.php

* Implement (now fixed) "recent_posts" function – get a list of recent posts for the sidebar.
* Fixed some CSS problems with h1 in the error/install pages.
* Added support for more routes to Cascade module.
* Fixed misbehaving and deprecated `preg_replace` functions in Admin.php

![screen shot 2014-04-16 at 23 16 45](https://cloud.githubusercontent.com/assets/4855211/2736527/9bbf6fa2-c66e-11e3-92b7-09030176c721.png)
![screen shot 2014-04-10 at 21 58 08](https://cloud.githubusercontent.com/assets/4855211/2736526/9b8393c4-c66e-11e3-8a62-ffa66508dd57.png)