Message with verbosity 0 leads cocaine-runtime

to segfault as nullptr is sent to a stream.
[Logging] Logging functionality has been completely refactored.

Now Cocaine uses the following Blackhole features:
 - Scoped attributes guard for keeping common attributes while some object lives (see 'bootstrap' section, for example).
 - Logger wrapper for source attribute keeping.
[Logging] Using attributes more widely.
Drop duplicate typedef.
Fixing the build, I hope.
Merge pull request #110 from noxiouz/fix_convert_verbosity_more_gently

Message with verbosity 0
[Logging] Fix issues.
[Logging] Synchronize.
[Logging] Repository is now being logged.

Also some refactoring done.
[Logging] Source renaming.
[Logging] Make available some other combinations of formatters/sinks.
[Logging] Synchronizing.
[Logging] Typo fix.
Merge pull request #112 from 3Hren/master

Logging Improvements
Log message wording.
Beautifulization.
Factor out the defaults.
Create logs using the Context functions.
Fixed a couple of log messages.
Refined log messages in the Repository.