add scaffold for rocks
add controller tests for rock
add rock to region
database migration run
test that regions hold either rocks or other regions
test that region is not assigned itself as child
add test for parent region
add validator for region parents and childs

this validator keeps regions from being their own parents or childs
in the region tree.
add validations for the region tree

Only leafs of the region tree are allowed to hold rocks. These
validations make sure that invariant is always true.
show rocks on regions#show
Only show top level regions on regions#index
display regions on the homepage
Apply Rocks to a region based on the region_id

Provide a nested route for rocks and base the region for a rock on the
region provided within the route.
Disallow Rock creation without Region

This deletes the routes to rocks#new and rocks#create that are not nested.
It also deletes the nested rocks#index etc. routes.
add test for editing a rock
Merge branch 'rocks_feature'

The branch adds a Rock model and a RocksController. Rocks belong
to regions and can only be added to leafs in the region tree.