By default, transactions are used to check metadata, and possibly
reopen the db, to get a current db handle. However, if a `max_age`
option is provided and db handle was checked less than `max_age`
milliseconds ago, use properties from that cached handle instead.

The main use of this feature be in pluggable authorization handlers
where it might be necessary to inspect the security doc multiple times
for the same request before a final decision is made.

`revs_limit/1` was updated as well, mainly for consistency since it is
almost identical to `get_security/1`.

Integrate emilio - erang linter

Merging it on the grounds of CI pass and +1 in the original PR. 

Add tests for view cleanup.

If a client notices that a job has failed we restart it. If a job failed
for a different design document id then we resubmit the build request.

Each registered index type can now get a signal on when to clean up
their indexes.