New File Wizard

I finished the new wizard, with exception of one remaining problem, you can now check out if it works on your machines too. Finally I found a way to inject the new wizard elements into the wizard registry (see class `RegistryExtender`). The injection is done with reflection but is very safe to my understanding.

The remaining problem is that in the "New" menu, which is shown in the Scala perspective, the new wizards are not shown (but the old removed ones are). See https://github.com/sschaef/scala-ide/commit/5800e1bf5cfcdfb37fc83b3dd8c600f4e94fa482 for a more detailed explanation. I didn't find a way to change the wizard entries of a perspective so far - but hopefully I will in the next days. If someone knows how to do it please speak up.

I removed the old wizards already, maybe this breaks an IDE extension, I didn't verify that yet. But updating an extension shouldn't be difficult.

Review by @skyluc at least
2 things I don't follow about this method:
* why does the `FileCreator` have to create the file itself, instead of generating an `IPath` and letting the framework creating the file? It seems to me that the file creation will be always the same, as long as the path is known.
* why having a different code path for files created in source folders and outside of them? I don't really see what is gained. The string manipulation is likely different, but it is still necessary.