Properly name SB_Sidebars.php

typo: was missing "e" in "Sidebars"
Update opening doc for sidebar manager
Update classname and instantiation of SB_Updater
Create SB_Breadcrumbs placeholder
Hook our file inclusions and translations up to init
Add a temp SB_Settings class placeholder
Move images directory
Reintroduce THEME_OPTIONS and THEME_PREFIX constants