Switch mustache to handlebar or something to allow template inheritance

[Drakulix]

We have a lot duplicate code in our html templates. Mostly between index.html and package.html.
This could be reduced grately, if the template language had something like inheritance or an include statement.

Mustache does not seem to allow for it. Handlebars might be a suitable replacement, but anything that does not move too much logic into the templates is fine.

Edit: https://github.com/sunng87/handlebars-iron looks suitable.