Add SqlAction.getEventLogPercent method

This method provides the raw percentage used by
Kenny's reindex script but at the API level.
Add ome.services.metrics package

As a very thin wrapper over com.codahale.metrics,
this package provides a number of ways to track
server-side happenings.
Provider getter for PersistentEventLogLoader key
Integrate metrics into Indexer

With this commit, once an hour (and constantly via JMX),
the indexer provides metrics on how long each batch is
taking and how close to "completion" (i.e. being up-to-date)
it is in a unix-style 1min,5min,15min split.
Handle null metrics in Indexer
Add metrics support to PixelData
Include percent calculation in timer
ibiblio only contains metrics 3.0.1
Fix maven cache

The differences in layout of the .m2 cache lead to weird
results. Jars were being downloaded successfully but then
no longer found by ivy.
More fixes for .m2 cache

There were a few typos in the cache
specification which may be related,
but likely the overall problem that
we're seeing is:

  https://issues.apache.org/jira/browse/IVY-1088
Hack: disable pom usage for downloaded resources

I have no idea why this is necessary, but with poms
activated, `ivy:retrieve` doesn't symlink any jars
under target/libs despite the fact that the files
**are** downloading under `~/.m2`. This is certainly
suboptimal and more complex requirements will likely
fail if we ignore their dependencies, but this does
allow the metrics jar to be available.
Move ome.services.metrics to ome.system
Add metrics to PixelsService
Minor SqlAction javadoc fix
Merge pull request #2638 from joshmoore/rebased/develop/add-metrics

Add metrics (rebased onto develop)