Improved web administration module

This pull request improves the web administration module. See [the commit message](https://github.com/dhoepelman/Alitheia-Core/commit/33819a93a839be7deee67c93709f65778039d153), the documentation in [/doc/developer/webadmin](https://github.com/dhoepelman/Alitheia-Core/blob/master/doc/developer/webadmin/developing_webadmin.md) and the [report](https://github.com/delftsre/assignments-2013/blob/master/1521969-4016009/Report2.md) which was written in context of the TU Delft Software-Reengineering course