[counters] Improvement of the mono counters API

 - now support differents types, units
 - retrocompatible with the previous API
 - update some gc and thread counters to use this new API
 - multiple data sources (system data, ...)
[counters] Added mono counters to log profiler

 - Added interval parameters to set sampling frequency (in ms)
 - Updated decode.c/mprof-report to show counters grouped by category or time
[counters] Add performance counters as data source for mono counters