Switch to rapidpro/rapidpro

[smn]

This PR:

• switches to tags now published on rapidpro/rapidpro
• adds a few standard docker container labels
• adds a temporary work around for pip & setuptools breaking builds, see https://github.com/pypa/setuptools/issues/942.

Was originally reported in #8.

[smn]

These builds are failing because of issues in rapidpro, see https://github.com/rapidpro/rapidpro/pull/445 and https://github.com/rapidpro/rapidpro/pull/446 for the fixes.