Make default metrics handling more robust

CRU_REVIEW has a cru_metrics_version field which is expected to be a non-null integer.
The field is populated when creating a review, with the highest metrics version (from cru_metrics_version). This in turn starts out empty and is pre-populated from default-metrics-config.xml in FISHEYE_HOME. If the file doesn't exist or is malformed, reviews with null cru_metrics_version are created, causing subsequent NPEs on code paths expecting the field to not be null.

• verify and improve robustness of the default import (couldn't it just come with data.sql/upgrade task)?
• fix error handling if the metrics version is not resolved correctly (should throw and prevent creating broken reviews)