Remove magic for loading templates from module names
Fix tests to use full template names
Remove duplicate traitlet definition
Drop unused traitlet imports
Move html templates into separate folder
Use _default method instead of redefining trait
Remove extraneous template argument from test
Walk nbconvert templates directory for package data files
Fix glob pattern for nbconvert template files
Merge pull request #4727 from takluyver/nbconvert-template-magic

Remove Nbconvert template loading magic based on module name.

A little more explicit now, plus a few traitlets cleaned up.