Added a TagProcessor

The TagProcessor adds the tags key to the record making it so that it can be used by handlers like Raven.
Updated the RavenHandler

It can now make use of the tags processor to display tags inside Sentry. It can also include tags that were specified in the context.
Update TagProcessor.php

Array merge was unnecessary since it is not set anywhere else than here.
Create TagProcessorTest.php
Added a test for Tags
Update RavenHandlerTest.php
Update RavenHandlerTest.php
Fixing the Undefined index error
Update RavenHandlerTest.php
Update RavenHandlerTest.php
Update TagProcessor.php
Update RavenHandler.php
Update TagProcessorTest.php
Update RavenHandler.php
Merge pull request #347 from ipsq/master

Added tags for Raven