Generate asset urls with a function
Add asset prefix to create args
Factor out duplication in url joining functions
Merge branch 'master' into serve-assets-with-static

Conflicts:
	lib/filters/__init__.py
	lib/templates/__init__.py
	templates/base.html
	test/filters/test_filters.py
Merge branch 'master' into serve-assets-with-static

Conflicts:
	lib/filters/__init__.py
	test/filters/test_filters.py
Merge pull request #41 from alphagov/serve-assets-with-static

Serve assets with static