Add additional route to allow writing by data group/type

- updates integration test for exception handling
- posting to bucket by name or by group/type resolver should work the same
write a comment
@wip feature test
Merge branch 'master' into write_api_accept_type_and_group

* master:
  More explicit on how to replicate the DB
New step to allow posting with a path
check for bucket name
do not print
Merge pull request #196 from alphagov/write_api_accept_type_and_group

Write api accept type and group