Deduce the template path
Deduce the template path

Instead of having the course author have to remember the full c4x path
of the template, deduce the asset path and let them just input the
filename.

arbrandes/hastexo-xblock,hastexo/hastexo-xblock,arbrandes/hastexo-xblock,hastexo/hastexo-xblock,arbrandes/hastexo-xblock,arbrandes/hastexo-xblock,hastexo/hastexo-xblock,hastexo/hastexo-xblock,arbrandes/hastexo-xblock