cubicweb #1171 cubicweb-ctl command to analyse performance [open]

here is the scenario:

1/ turn on rql logging in all-in-one.conf

2/ use the application to stress it a bit

3/ run cubicweb-ctl perf myinstance to print a report about performance

PS: look at cubicweb/devtools/exlog.py and use it as a basis for this command