Created Moon model

Start working on issue https://github.com/Mischback/django-oweb/issues/27
Added Lunar Base (Station41)
Added Sensor Phalanx (Station42)
Added Jump Gate (Station 43)
more buildings

Created all necessary buildings for a moon. The shared buildings have been subclassed, to make them assignable to a moon.
Fixed a bug in Home-view

``get_list_or_404()`` was used, but this makes no sense, if the user has no accounts... We must show the standard list (even if it is empty) and provide the possibility to create a new account.
Yeah, actually show that account creation link
Merge branch 'hotfix01' into development