Use XDG Base Directory Specification

Use local directories to store data and cache according to the XDG
Base Directory Specification:
http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

This mainly means that the manifests are now stored under
~/.local/share/inqlude/manifests, not ~/.inqlude/manifests anymore.

Fixes #21
Update roadmap
Use KDE git URL

Inqlude now pulls from the canonical data repository for Inqlude
on the KDE git server. The GitHub repository will continue to
exist to make it easier for non-KDE people to contribute.

This commit also slightly cleans up the pull logic to not delete
existing directories anymore, if they are not a git repository.
Update version number for alpha release
Clean up dependencies

* Define all dependencies in the gemspec file
* Get rid of obsolete TestUnit dependency
Remember to change the alpha/beta ribbon