feat(controller): support for application key/value tags
feat(client): support for application key/value tags
chore(controller): fix south default values with a data migration
feat(tests): integration tests for tags, move limit tests under config
Merge pull request #1665 from gabrtv/tags

Application tags for scheduling to specific hosts
feat(*): add `make test-style` targets

This gives us an opporunity to run code checkers and linters as part
of testing, as we used to on travis-ci.org. By default, unit tests
will check code syntax and style first.
ref(*): clean up Go and Python code for `make test-style`