Keep the storage alive in Router group management.

When initializing or refreshing the routing groups, keep the storage reference
alive so that we won't re-initialize it for every group we got from the group
lists.
Don't cache routing groups as it's impossible to

update routing groups without cleaning cache by hands.
Get rid of group_t struct.
Merge branch 'noxiouz-disable_group_cache'
Drop unnecessary public typedef.
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.