infrastructure to support asynchronous discovery of Rmd templates
add stubs for template discovery widget and server front end
plumb asynchronously returned template folders to UI
show friendly template name in dialog
style and layout for New R Markdown dialog
end-to-end functionality: create drafts from template specified in dialog
add some progress indication and error handling to template discovery
handle case where no templates exist
don't accept input if user hasn't chosen a template
use settings in template YAML in New R Markdown dialog
emit name of template's owning package to client
show source package with template name
add help link to template list
don't show template create options when there are no templates
create template directly rather than emitting draft command to console
add icon to From Template entry in New R Markdown dialog
save the path to the user's preferred template and default to it
show template description as tooltip
split template folder output lines correctly on Windows
use a progress indicator when creating a document from template