refs #44 status class
refs #44 dynamical status variables from gcs backend
refs #44 null termination
refs #44 - some evs statistics, histogram improvements
regs #44 - cleanups
refs #44 - dynamical status variables implementation

Currently implemented for gcs backend status gathering. Status class
is simple string based key-value store, which is appended to the
wsrep_status_var array.
Merge branch 'gh44' into 2.x