urls: import the whole module rather than single views.

We import all the views anyway, so we end up repeating every name twice,
and potentially polluting the namespace.
Merge pull request #46 from mgorny/views-no-import

urls: import the whole module rather than single views.
Move middleware & installed app settings to common.

Keeping them split into all those samples is not really beneficial,
and makes bisecting painful. Instead, keep the common middleware & apps
common, and override as necessary in devel/prod.
Merge pull request #49 from mgorny/merged-settings

Move middleware & installed app settings to common.