New File Wizard - final version (hopefully)

Thanks for the review in the last PR, I reworked the wizard a little bit (last 6 commits are new, some are rebased/removed). Main points:

- Project selection is replaced by source folder selection
- Files are created by the wizard and no longer by the file creator
- Old wizards do now coexist with the new one. There exists only a single entry for the new one, called "New Scala File"

The empty file creator is still broken for some cases, but it can be resolved after M3 together with all other outstanding issues. If I have not overseen something critical this PR should now be ready for M3.
I'm not sure if I like the serie of `map` call. At least the `p`s should be replaced by something a bit more meaningful. Like this it is a bit hard to know what the closure is applied to.

I tried to transform it in one `map` call, but it is not way prettier:

```scala
       .map{ srcDir =>
          val reducedPath = if (isDirectory) {
            path.removeFirstSegments(srcDir.segmentCount())
          } else {
            path.removeFirstSegments(srcDir.segmentCount()).removeLastSegments(1)
          }
          if (reducedPath.segments().length == 0) {
            ""
          } else {
            reducedPath.segments().mkString("",".",".")
          }
        }.getOrElse("")
```