Rewrote SB_Sidebars->get_custom_sidebars() much more efficiently
Updated sidebar tranansient buster to support new full-length taxonomy key
Much better setup for retrieving custom sidebars and determining if they replace the existing sidebar

Still needs work for primary and secondary widget areas, specifically
Minor tweak to inline docs on sidebar.php
Fixed the transient deleted when custom sidebars are edited
Updated the registered ID for our Primary and Secondary sidebars
Moved upgrade routines back to startbox.php (because they need to run regardless of whether admins allow for automatic updates or not). Added upgrade steps for 2.7
Updated changelog to reflect the custom sidebar fix
Typography tweak for heading elements. Fixes #19
Version pushed to 2.7