Allow fields to be retrieved from classes (mostly for testing and general sanity).
Add test showing problem with double-inheritance (fields from classes below the first are accessible but not in the list of fields (and so not validated).
Fix support for double-inheritance of config fields.
Merge branch 'feature/issue-695-fix-support-for-configs-with-double-inheritance' into develop
Add transport_name to SMPP service tests that were missing it (this was always meant to be mandatory but only became required after the config fixes in #695) (@jerith).
Merge branch 'develop' into feature/issue-693-change-the-twitter-transport-to-use-txtwitter