Support configurable template data languages

This pull makes Handlebars/Mustache a full-fledged template language, supporting templating of any language (default is still HTML).
* "Settings->File Types" now allows configuration of which language is being templated by choosing a "Registered Pattern", clicking edit, and choosing a language from the dropdown
* "Settings->Template Data Language" settings will now be respected, allowing configuration of template data languages by project and folder
* "Settings->Handlebars/Mustache" can now configure which language's comment syntax is used by the "Comment with Line Comment" and "Comment by Block Comment" actions

This pull request closes #26.