Fixed package path in testsetup.

The testrunner wronlgy searched the complete project, so also the `src` directory for tests, which end in import errors. With this change the runner only runs test from the opengever.core package.
Fixed backref name of the groups_user join table.

See https://github.com/4teamwork/opengever.ogds.models/pull/4 for more details.
Added missing kgs inclusion.

The commit #9cba578e9105ab15ab20f58179e4563db9786ca9 dropped the
opengever-zug kgs inclusion, which is right, but it dropped the
complete inclusion of the kgs version. The standard opengever
version pinings are necessary.
Merge pull request #236 from 4teamwork/pg_add_misingkgs_inclusion

Added missing kgs inclusion.
Merge pull request #233 from 4teamwork/pg_fix_backref_name

 Fixed backref name of the groups_user join table
refactor, get rid of `contact_info.get_email2`.

This method was called from exactly one place.
It handled 6 different kind of inputs but the only reference
called with with only 2 distinct inputs. Those inputs then
both share the same duck-type interface.

There is no need for indirection, which is not used.
refactor, get rid of `contact_info.get_email`.

This is a follow up to: #228.

This method was only called from two places.
We inlined both. This allows us to drop this "heavy-switching-logic".
Refactor `contact_info.get_client_of_inbox`:

- Use the `get` method instead of a filter_query statement.
- Drop unnecessary determination (queries on the primary_key only returns 0 or 1 result).
Change client query using `get` instead of `filter_by`.
manual revert of 26302a50. That "workaround" is not required.

There was a check to work around collation issues with Oracle.
The reason to add this behavior, were duplicated records with different case.
The `clients` table is only filled by opengever. We need to maintain consistency
of case ourselves to make quering easy. Having two records with the same primary_key
in different case is going to break the application anyway.

/cc @lukasgraf
use `get` when only filtering by primary key.
Reworked is_group_member, so that it only use one query.
Refactor get_user_sort_dict.
consistend use of `filter_by` for single table queries.
`get_group_of_inbox` returns `Group` object.

As the name suggests, this method fetches the whole group.
However it only returns the `groupid`. This patch returns
the complete group object instead.
use `is_one_client_setup` where appropriate.
`count` instead of fetching the record. We only need to check existance.
Removed IMailInAddress behavior. Not needed any more with ftw.mail 2.0.
Provide an IntIdResolver adpater to generate Dossier Mail-In addresses

based on IntIds, and use it instead of the old implementation.
Removed og.mail IMailSettings registry interface (now done in ftw.mail).

Added upgrade step to migrate settings to ftw.mail's IMailSettings and
remove old og.mail IMailSettings.