Submit all widget control inputs outside of the .widget-content
Export dimensions, filter is_wide, and if so add class to container
Add slide-out widget panels over preview for wide controls
Construct newly-added wide widgets as wide
Strip widgets from sidebars_widgets[] settings if not registered

A widget added to a sidebar leaves its widget_id in the sidebar even
when the widget goes away, for example due to a plugin deactivation.
Now any such widget remants will get filtered out when sent to the
client.

Without this fix, a JavaScript error would be thrown:

> Uncaught TypeError: Cannot read property 'transport' of undefined
Collapse any expanded wide widget controls when opening addition panel
Show only one expanded widget control at a time

Prevents abundance of expanded widget controls from cluttering up the customizer.
Solves problem of wide widget controls from appearing over each other.

When one wide widget is expanding while another is collapsing,
the expanding one will always have a higher z-index than the collapsing one.
Eliminate hover/focus styles added to help when multiple wide controls were open

Made obsolete by e7107f583, which only allows one widget control to appear at a time.

Reverts part of 478fb21ff
Keep wide widget control positioned vertically with widget-top

Fixed-positioned widget-inside keeps position when scrolling,
resizing the window, and when reordering widgets in the sidebar.
The widget control remains in view even when the widget-top is
scrolled out of view.
Make wide/normal widgets toggle at same speed

Refresh position of wide widget when another widget collapses (or expands)
Merge pull request #89 from x-team/wide-widget-controls

Add support wide widget controls