Adds Confirmation popups for duplicate files errors

- ProjectManager: renaming a file to a name that already exists
- ProjectManager: moving a file into a folder with a file that has the same name
- Refactor->Rename: when renaming a type leads to a file rename, and that file already exists
Merge pull request #348 from Gama11/DuplicateFileError

Add Confirmation popups for duplicate files errors