CodeChecker parse command should provide fast checker statistics

[dkrupp]

To get rid of the noisy checkers, the users wants to list the number of reports per checker and switch off the most noisy checkers. There is no convenient way in the CodeChecker command line to query the number of findings per checker. The parse command prints this, but in the case of 100 000 reports the parse time is above 15 minutes, which is far too long. One would expect such statistics to be printed in less than 5 seconds.

CodeCheker should provide a
CodeChecker parse --checker-statistics -d 3
command which would list the number of reports (as it would appear in the web GUI non-unique mode) per checker.
-d is the depth switch.
-d 0 statistics is printed on the main directory
-d 1 checker counts are printed on all directory separately
-d 2 checker counts are printed on teh 2nd level directory level
-d -1 checker counts are printed on the file level