templates:
- add placeholder footer.html, head.html templates
- allow 'base_html', 'footer_html', 'head_html', 'header_html' to be added via wb-manager 'add-template' cmd
- automatically add 'base.html' when adding a copy of other templates, as jinja2 extends looks for templates locally
ui tweaks:
- vueui: support logo loaded from ui.logo
- make logo link to home page
- home page: don't show collection title if title is empty
documentation tweaks:
- clarify static_path is for loading path
- clarify footer and head templates are empty by default
- remove extra is_framed from top frame template documentation
bump to 2.7.0b1