Filter manufactureres in license.

Added:
- field manufacturer to license search form and updated tests,
- flake8-debugger to travis (checks for 'pdb' and 'ipdb' string (https://pypi.python.org/pypi/flake8-debugger/1.1)).

Removed:
- AssetManufacturer lookup & replaced it with ManufacturerLookup,
- search_licence.html template.