Design admin interfaces

[tobyzerner]

This is subject to the finalization of #1.

The administration interface will be wrapped in the default theme. It will be broken up into separate "panes", listed in a sidebar — something like:

• Dashboard: flexible "widgetized" interface (similar to OctoberCMS dashboard)
• Settings: forum title, default language, basic settings
• Appearance: change the colours of the default theme, or change to a different theme
• Permissions: manage user groups and permissions
• Extensions

What needs to be done:

• Define the contents of each pane more precisely
• Mock up each pane

[tobyzerner]

Mockups are done. Will post them when work begins on the admin section.