replaced rapidsms.tests.__init__ magic with a custom suite
replaced rapidsms.tests.__init__ magic with a custom suite

i was manually keeping __test__ up to date before, which was a bit janky
and surprising, so i refactored it properly. now all of the modules that
we wish to import unit tests from are simply imported. both regular unit
tests and doctests are run every time './rapidsms test' is started.

caktus/rapidsms,ken-muturi/rapidsms,dimagi/rapidsms,ehealthafrica-ci/rapidsms,unicefuganda/edtrac,dimagi/rapidsms-core-dev,lsgunth/rapidsms,unicefuganda/edtrac,catalpainternational/rapidsms,lsgunth/rapidsms,rapidsms/rapidsms-core-dev,peterayeni/rapidsms,catalpainternational/rapidsms,ehealthafrica-ci/rapidsms,ken-muturi/rapidsms,peterayeni/rapidsms,catalpainternational/rapidsms,lsgunth/rapidsms,eHealthAfrica/rapidsms,ken-muturi/rapidsms,eHealthAfrica/rapidsms,unicefuganda/edtrac,rapidsms/rapidsms-core-dev,caktus/rapidsms,dimagi/rapidsms-core-dev,eHealthAfrica/rapidsms,peterayeni/rapidsms,dimagi/rapidsms,peterayeni/rapidsms,ehealthafrica-ci/rapidsms,lsgunth/rapidsms,caktus/rapidsms,catalpainternational/rapidsms