Instead of processing the input further and forwarding the
credentials to prosody, we catch the error early on to prevent
having to handle the 400 error code specially and to prevent the
password from spilling in other components.
Fixes#55.
- Avoid fighting import cycles using a factory function
- Collapse useless subpackages into simple modules
- Move flask plugins / infrastructure in own module
- Refactor how blueprints are used to localize information about
URL routing to app factory
