Added without_assisgned_location field to dc-search form.
Enables to search dc-assets without location fields.
Location fields are: data_center, server_room, rack, etc.
Merge pull request #520 from xliiv/no-location-in-search-ok

Added without_assisgned_location field to dc-search form.
Merge branch 'develop' into no-slot-validation

Conflicts:
	src/ralph_assets/views/search.py
better var name: asset_without_category_and_location