Properly ensure that the token exists and add defensively check for a
non-nil value.

Closes #4294

The introduction of ActiveJob and `deliver_now` in 7f214cee caused a race
condition where the mailer would be invoked before the project was committed
to the database, causing the transfer e-mail notification to show the old
path instead of the new one.

Closes #4670

This is needed to support Huboard and a generally useful value.

This method can be used to filter projects to those visible to a given
user.

- Enable CI by default for all new projects

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

When project is updated and it is a fork, then visibility_level
should not be less restrictive than in its parent project.

refactored permissions and added update_project_member ability logic. Also refactored owner methods to a concern.

By using a JOIN we can remove the need for using 2 separate queries to
find a project by its namespace. Combined with an index (only needed for
PostgreSQL) this reduces the query time from ~245 ms (~520 ms for the
first call) down to roughly 10 ms (~15 ms for the first call).