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
You shouldn't have to create you own completion overlay. There is one provided by Eclipse for `Text` field.
There is an example in the compiler settings preference page [CompilerSettings.scala L394](https://github.com/scala-ide/scala-ide/blob/master/org.scala-ide.sdt.core/src/org/scalaide/ui/internal/preferences/CompilerSettings.scala#L394).