Abspath

ref. to https://github.com/Codiad/Codiad/issues/248

- added constant WHITEPATHS to restrict abspath projects to certain root paths
- missing abspath structure will be created if not exist
- abspath will be checked for read/write permission before it will be created
- added simple confirm dialog if you want to create abspath project instead of workspace folder (dont know if this is really required?!)
- new class common which other classes can extend from