[git] cleanup
[git] reuse parent logger
[git] cleanup
[git] suppress stdout by default

review all commands and unsuppress stdout for some certain ones.
[git] log suppressed output by separate logger

This allows to enable git4idea debug log and avoid massive output
from git log etc.
If the whole output is needed, it can be enabled by separate logger
with the "output" prefix.
Prefix is used instead of suffix, because loggers are dot-recursive,
i.e. enabling git4idea.GitHandler would enable git4idea.GitHandler.out.