Use Handlebars in document list

I use Handlebars instead of Mustache in document list because there it
first-class support in the asset pipeline.  The associated asset
pipeline plugin allows to define requirements for Handlebars templates
which are then available as JavaScript object.

Doing so, I remove the Mustache templates from the HTML file and create
separate template files in grails-app/assets/javascripts/templates.  I
also do not any longer distinguish between the breadcrumbs navigation
and the document list.

Furthermore, I fix some issues in the document list.