XD-54 - XD Metrics backed Message Counter
add pool configuration to Jedis and see if redis tests pass on CI server.
Introduce Metric and MetricRepository interfaces.

Reduces CounterRepository, GaugeRepository to marker interfaces
and removes boilerplate from in-memory implementations.
Re-enable tests for MessageCounterHandler.

Other redis tests have already been re-enabled so no point in
ignoring this one.

Fixed typo in GaugeService.
Fix metric names.
Add deleteAll method to MetricRepository.
Refactor Redis repositories.

Pull methods up into base class to remove duplication.
XD-66: Use metric name for equals and hash code.

Removed non-final data and added tests for adding instances to
a HashSet and making sure they don't disappear when the data is 
changed.
Deleted outdated Intellij module file.
XD-66: Basic "RichGauge" implementation.

Support for a gauge with max, min and mean values.
XD-45: Remove expiry settings for redis metrics.

These aren't currently required.

Also minor changes to Gauge and Counter services to make them
throw an exception for missing instances