End user mode in level editor

Currently there is one version of the level editor. We have two very distinct use cases for the level editor, however:
1. End users use it to create levels to play and share with others. ("end user editor")
2. We (joyridelabs) use the editor to build our commercial episodes. ("advanced editor")

We want to have two different modes for the two different use cases. Everybody will be free to switch between the two modes anytime, of course. The main differences are:

- The end user editor won't allow to manipulate anything but the (physical simulated) main layer. Backgrounds and foregrounds can be chosen from a set of predefined level templates.
- The advanced editor will not be polished. So expect dirty hacks, crashes and eating of puppies. This will basically just be an internal version for joyridelabs, that we don't want to hide.