[tools] Refactor compare and benchmarking suite

Compare :
 - add .json to results file to allow filtering based on their name (avoid loading of non JSON file, which generate an exception)
 - remove loading of benchmarks and configs file when passing --no-run
 - use Xamarin colors (https://github.com/xamarin/design#colors)

Agent :
 - store counters in a separate file to reduce drastically memory consumption
 - load counters into a cache, so it does not crash when we load a lot of results files, while still reducing number of JSON deserialization.
 - do not store benchmark output : make debugging through jenkins way easier, and does not bloat the amount of data stored
 - store commit date with Revision, so it is easier to sort