monitor: using handystats library to gather runtime statistics

 - instrumented process_raw and cache
 - compile time option WITH_STATS allows to enable/disable handystats
   instrumentation at compile time (WITH_STATS is ON by default)
 - integration into monitor service with new category "stats"
   (native, http, python binding)
 - config: "handystats_config" option bears the name of handystats config
   file, could be omitted, handystats will run on defaults then
debian: build dependency on handystats >= 1.8
monitor: complete replacement of react