Avoid costly NOT IN filter on an empty list
Remove superfluous underscore from notified_users
Make task table name plural for consistency

All other table names are plural already.
Merge pull request #173 from guidow/table_rename

Table rename
Merge pull request #172 from guidow/avoid_emtpy_list_filter

Avoid costly NOT IN filter on an empty list
adding master.api.agent_updates to docs
Increase attempts on setting agent, not state

The previous code would increase attempts every time state was set to
"running". This turned out to be a bad idea: The running state is set by
the agent, not the master, and there are a lot of possible failures
where the task never gets set to running in the first place. This would
lead to the task being retried over and over again, because it would
never reach its retry limit.

This code increases attempts on assignment of an agent, which avoids the
endless retry, but has the disadvantage of increasing attempts in the
case where a task gets assigned to an agent that is offline. (Which can
happen if the master has not yet realized that this agent is offline.)
Remove test that broke on the last commit
Merge pull request #174 from guidow/inc_attempts_on_assign

Increase attempts on assigning agent instead of setting state
Job titles do not need to be unique after all
Merge pull request #175 from guidow/job_title_not_unique

Job titles do not need to be unique after all
Convert a few more places to use UTC for times

Addresses #117
Merge pull request #176 from guidow/utc_conversion

Convert a few more places to use UTC for times