Finalized translating all strings.

This does not yet issue #35, because translated items are not loaded
for all Nibs. This will require my own copy of DMLocalizedNibBundle
instead of having it as its own subproject, plus possibly a subclass of
NSViewController or something.
Add own version of DMLocalizedNibBundle

Part of #35. This ensures that objects loaded through newer methods
still get translated properly. For some reason it does not currently
work for view controllers, though.
Localization loads properly for all Nib files.

What surprises me is that I never encountered this issue in other apps.
Or did I, and I just never noticed? That would be embarassing.

Almost done with issue #35.
Full localization for all parts (in German only).

This fixes #35. While the current version is German only, it is now
possible (and relatively easy) to add more languages.