Previously, some kinds of errors would throw nice and fun cascades
of exceptions.
We now have a nice, clean error page for 500 and 503 (backend
connectivity) errors which includes minimal debugging information
for productive setups and a traceback for development setups.
In any case, the full exception is logged to the log with an error
ID which is printed on the error page.
- 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
