Steps to reproduce the issue

Try to perform menu item assignment from a template style edit page, using the Menus assignment tab. You get a javascript error when trying to use the toggle buttons: $$ is not a function.
IMPORTANT: this will not happen with Joomla default template (ie Beez), though the problem is indeed in Joomal and not in external templates

Expected result

Working assignment

Actual result

Javascript error

System information (as much as possible)

Joomla 3.4

Additional comments

Looks like mootools is needed in /administrator/components/com_teplates/views/style/tmpl/edit_assignement.php. However, it is not explicitely loaded by com_templates, which leads to the error.
This problem is hidden in Joomla! default templates because both of them have a "media" field in their params, which requires mootools and does load it. However, any template that doesn't have such a field will fail (I'm using Yootheme's yoo_katana for instance). Again, this has nothing to do with the templates themselves.