Fix top widget padding and broken borders
Remove default live preview support from children of core themes
Close available widgets panel when previewed URL changes
Hide sidebar sections initially

Prevents FOIS (flash of inactive sidebars)

Fixes #36
Animate toggling of active/inactive sidebars

Fixes #9
Move logic for toggling customizer sections to parent

Eliminates use of cross-frame communication and instead uses customizer postMessage framework

Contributes toward #8
Auto-open sidebar section in customizer when accessed via notice on widgets admin

Fixes #32
Fix submission of selected widget with enter keypress on filter input
Put else statements on same line prev bracket
Provide a widget constructor option to opt-in to customizer support

This is an easier and more seamless method than adding a filter, which still an option.

Fixes #67
Improve phpDoc
Only trash previously-saved widgets

Prevent inactive widgets sidebar from overflowing with throwaway test widgets.

Fixes #46
Keep "Delete" link for new widgets; change to "Remove" when saved

Only when a widget is saved, does the link invoke a trash action.

Fixes #46
Bump version 0.12
Fix markdown formatting