Can't move or change functionality of buttons easily

To move the buttons or change the behavior of them within a search form or the nuxeo-document-create popup, a new element must be created that mimics the current nuxeo-search-form or nuxeo-document-create element.

Buttons and their corresponding functions should be changeable through a slot mechanism - same as the document-create and search-form templates - to make these customizations easier in the future.