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Deleted outdated Intellij module file.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