Implemented multi-files.

## Multi Files!
I implemented the multi-file setup, using `.cookie` as our file extension.
This simplifies the  code a lot and therefore allowed me to remove several Exceptions.

### Voting Time!
Whether or not we want a multi-file setup should be decided by everyone.
Hence the PR instead of direct commit to master.

But seeing as how this change fixes several errors and simplifies the code a bit,
*I would advice you to hurry up with voting* and possibly base further work on the changes in this branch.
(But please do leave the branch itself alone, or you will influence this PR).

See the commit message below for more details.

---
### The commit

Fix Exceptions (see issue #11).

Due to the fact that all java objects instantiate a FoldingDataEditorSupport.java, even when unopened or uneditable, we had a lot of exceptions.

This commit fixes those by deferring the instantiaton of a template provider until it is required and by checking if the file is writable.

Hide the toolbar when necessary.

The toolbar is now no longer visible on files that can not be templated.

We now have `.cookie` files to back up our application.
This means we no longer have in-memory files, file magic on close or need for the MainCloser.java.

It simplifies the code a lot.