Logging commun option for all commands

Add option for set level of verbosity :

option	level of log
no-option	"ERROR" level
-v	"WARNING" level
-vv	"INFO" level
-vvv	"DEBUG" level

Some of the messages has to be reviewed to set correct level of verbosity

There is a test command :

https://gitlab.inria.fr/sed-rennes/sharelatex/python-sharelatex/blob/logging_option/sharelatex/cli.py#L300

$ git slatex test 
effective_level=40
error
print
$ git slatex test -v
effective_level=30
error
warning
print
$ git slatex test -vv
effective_level=20
info
error
warning
print
$ git slatex test -vvv
effective_level=10
debug
info
error
warning
print