Add support for rendering basic HTML in TalkatuHistory.
* Remove the data argument from class methods
* Renamed TalkatuHtmlParser to TalkatuHtmlRenderer
* Created TalkatuHtmlPangoRenderer
* Use the TalkatuMessage::content-type to determine how to render the text in
TalkatuHistory.
Testing Done:
Tested in the demo with a hack for the content type that will be fixed in a later review request.