Summary:
Get rid of client class
Fix cppcheck errors
Add documentation to metrics.hpp
Add documentation to stats.hpp
Remove stats from global namespace
Fix build failures
Refactor a bit
Refactor stopwatch into a function
Add rpc execution time stats
Fix segmentation fault
Reviewers: mferencevic
Reviewed By: mferencevic
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D1200
