Test case for adding report metrics
Initial model and migration for session metrics
Renamed model
Parse metrics section from XML
Sort by ID, added method for grouping

Currently felt like not adding MetricGroup or such to DB, but still the
metrics need to be received grouped, so added a method that returns them
in groups.
Metrics can be shown

Added possibility to define report metrics which are then reported on
the report page. This is related to #22.

Going to add option for drawing trend line over some metrics. Also need
to fix merging so that the outcome of merged metrics makes sense.
Constraints and graph-column to metrics
Metrics summary data can be collected
Initial charting

Removed previously added metrics history data from Graph and added a
method for fetching history for each metric separately.
Charting code really added
Don't store duplicate metrics

In case user uploads multiple metrics by same group/name, remove the
duplicates by group/name. Possibly we remove the wrong ones but there's
no way to determine which to store.
Test import API with metrics
Merge API for metrics

Merge metrics in the same way as we do with feature/test cases already.
Test data
Don't try to concat if nil
For conventions sake enable hiding metrics section as well
Add column for hiding metrics
Enable hiding metrics section of a report
Test for hiding metrics via the API as well