Update user portal. Restructure base templates

The base template now provides a layout block that can be overwritten. A
new 'base' template is available for sidebar pages called
'sidebar_base.html' that implements the layout and forces it to be a
sidebar/main-content layout.

'sidebar_base.html' provides the 'sidebar' and 'main_content' blocks to
be overridden by impementing templates.
Restructure the templates directory