[1105892] Metric base unit in alert definition is incorrect resulting in bad absolute metric threshold evaluation
- fix issue where MeasurementUnits object was used where its String form was needed
- fix issues with keeping the units paired correctly with the selected
  metric, and ensure the first list entry is always the default.
- simplified the widget initialization (although this was not a primary issue)
Merge branch 'master' of github.com:rhq-project/rhq