Pluginsystem

Completely rewirtes EntityProps, makes them able to be edited in the IDE.
Adds Plugins.

Is subject to be under further development in the next time - this PR is just to review (I will rewrite some things..)

![plugineditor](https://cloud.githubusercontent.com/assets/5982050/4108739/e76177e2-31db-11e4-8870-aa5b94236753.PNG)
![sheetineditor](https://cloud.githubusercontent.com/assets/5982050/4108738/e7601bb8-31db-11e4-89b0-7f0dcd08de75.PNG)