Made use of OrderedDict compatible with py26
Add exception `ConfigurationError`
Add extra checks of user input
Remove access to raw json, add access to matrix

The raw json data shouldn't be accessed, but the matrix version of data will be
useful for testing (no need to parse CSV on each test).
Generalize prettifying of metric names.
Fixed bug when reviews were not showning

Also put the review format into a global constant.
Added tests for the GroupMetricsTable