Added CategoryErrorLevelActivationStrategy, which enables setting the
Error Level threshold per log channel.
Refactored / Renamed the CategoryErrorLevelActivationStrategy to the
more appropriate ChannelLevelActivationStrategy.
Fixed phpdoc, typo and indentation issues.
Merge remote-tracking branch 'netmikey/master'
Fix a few details and add docs to the ChannelLevelActivationStrategy, refs #186