Refactor [SymfonyInsight] to new service model and rename (#2572)

Based on some discussion/feedback here, this PR now contains several changes:

* Renames the `Sensiolabs` badge/service content to `SymfonyInsight` to reflect the rebranding of that product/service
* Refactors the original service to the new service model (using `BaseXmlService`)
* Updates the color scheme of the original/initial badge type (SymfonyInsight Grade) to more closely mirror the colors used by the vendor/service provider
* Adds a new badge type (violation counts/summary) 
* Adds both mocked and live tests (there were none before) for both the grade & violation badges using the new path `symfony/i` as well as a couple tests for the old path `sensiolabs/i` to check for backwards compatibility

Refs #1358