Support configurable template data languages

Remove all assumptions that we are in an HTML file, and start
respecting the user's template data language selection from
"Settings->Template Data Languages"
Enable File Type template data lang selection

Give HbFileType the correct marker interface (TemplateLanguageFileType)
to enable selecting a global template data language for each file
extension in "Settings->File Types->Handlebars/Mustache".  This
also enabled the "Change template data lang to..." quick fix
for errors in templates
Enable the "Change Template Data Language" action

Give HbFileViewProvider the correct marker interface
(ConfigurableTemplateLanguageFileViewProvider) to enable the "File->
Change Template Data Language" action for our templates
Make Commenter Language configurable

Add an option to select which language's commenter to use for the
"Comment with Line Comment" and "Comment with Block Comment" actions
in our templates.

This is needed since it doesn't look like there's a way to pass our
commenter context when it is invoked, so don't know what language we're
templating (and there's no proper comment construct in mustache).
This at least gives the user the option to have correct comments
for their most used template data language.
Merge pull request #37 from dmarcotte/all-langs-support

Support configurable template data languages