Always load custom controls file

* Fixes issue where preview pane didn't load correctly
Fix default object warning when adjusting Widgets panel priority
Add Main Column background image options to General > Background Image
Fix initial priority parameter when adding section options
Fill out existing color scheme options
Scaffold the Header panel definitions
Add mod file for Navigation section
Fix options variable carryover when adding sections
Fill out Header panel definitions
Add Logo section to General panel and rearrange other sections
Scaffold the Content & Layout panel definitions
Fill out Content & Layout panel definitions
Add Global section to Content & Layout panel
Fix prefix on Site Title section when panels not supported
Add Footer panel definitions