[Translation] Added logging capability to translator

[aitboudad]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#3015
License	MIT

[arodiss]

@aitboudad
psr/log contains interfaces only. You need to require some real implementation (most likely monolog/monolog) to have working logger

[inso]

Tested on my boxes and these changes add about 3% performance hit on page with ~260 translations:

# i7-3770
4.5958 ms vs 4.7394 ms (+0.1436 ms, +3.12%)
# Atom D525
25.9242 ms vs 26.6852 ms (+0.7607 ms, +2.93%)

Why not put all logging into LoggableTranslator and use it instead Translator based on 'kernel.debug' parameter?

[aitboudad]

@fabpot What do you think ??
I'm 👍 for LoggableTranslator, I'll try to do that tomorrow.
thanks :).

[fabpot]

@aitboudad Thanks for working on this. Unfortunately, translating methods being called a lot, we cannot add any overhead. Using composition to solve this problem (only in the dev env) is probably the best option (if possible). I'm closing this PR for now. If you want to work on a class that compose existing translator objects, feel free to give it a try and open a new PR.