Add support for Talk sidebar in public share pages

When the public share page is loaded "publicshare.js" is initialized,
which modifies the page to add a Talk sidebar. The default layout has
the header, content and footer in a flex column; when the sidebar is
added the layout id modified to still have the header and content in a
flex column, but the content is now a flex row that includes
"#app-content" and the sidebar, and the footer is moved inside
"#app-content" so it does not affect the sidebar.

The Talk sidebar includes a call container at the top, which is only
shown during calls, and below it a call button and a chat view which are
always shown.

The CSS styles are a mix of the styles for the public share auth page
and the Files app, as well as some rules copied from the main
"style.scss" file.

Signed-off-by: Daniel Calviño Sánchez <[email protected]>

css/merged-public-share.scss

@@ -0,0 +1,4 @@
+@import 'chatview.scss';
+@import 'autocomplete.scss';
+@import 'video.scss';
+@import 'publicshare.scss';