Allow question models to specify own button template

[swashbuck]

Subject of the enhancement

It would be useful to allow models to specify a different button template. Currently, this is hard-coded:

adapt-contrib-core/js/views/buttonsView.js

Line 41 in c7c74d4

const template = Handlebars.templates.buttons;

This would not be a new schema property and could only be set by the internal api.