Added TemplateRegionParser tests.

In the process, found a bug where if inside an html tag and scala code is used as attribute value, then any attribute names/values following the scala code are parsed as plain "xml content" because the xml parser loses the context it was previously in.
Renamed TTemplateEditor to AbstractTemplateEditor.
Replaced mistakingly used JSP action contributor with a template action contributor.
Added option to use old and new template editors.

There are a few quirks:
1. The icon used in the project/package explorer is always the icon of the default editor for the detected content type. As far as I can based on scouring forum posts and old eclipse bug tickets, this can't be changed to reflect the icon of the editor you actually open the file with.
2. HTML files now are displayed in the project/package explorer with the default template editor icon. This is because Eclipse doesn't handle well (at all?) multipart extensions (e.g. scala.html), so the content type extension point specifies the file-extensions as "html" and then further refines what files can be open using this extension point by specifies the file-names value with the regex "*.scala.html".
Fixed possible null pointer when performing HTML format action.

The format action doesn't format properly, but it doesn't prompt the user with a null pointer now :).