Fix bug where hwdoc subnav not always populated

Due to a set of missing parentheses and python's parsing model there
were cases where a url fields were not populated. This was introduced in
6c24e2b7 commit.
Fix bug where views with args PK's would fail

Introduced in b8276f91, int fields should not be in double quotes unlike
all other fields
Adding rack front, interior, back support

This adds three new fields in EquipmentModel model, namely rack_front,
rack_interior and rack_back with the respective meanings. They default
to True meaning that when adding new EquipmentModel that does not span
the entire U that should be unchecked. This closes #7