Widget base class: Adding function _toggleClasses from collapsible-widget-review.
addFirstLastClasses: Write the corresponding remove-method.

(cherry picked from commit b37d366033df1352e6cf9ee375b2f5d11bd3dc07)
Controlgroup: Implement "enhanced" attribute.
Demos: Controlgroup: Adding example of a pre-rendered controlgroup.
Controlgroup: Implement _destroy().
Controlgroup: Stop removing the legend upon _destroy().
Moving function domEqual to testHelper.

(cherry picked from commit def71da5e2331b533c5c958472ebed74275486fd)

Conflicts:
	tests/unit/select/select_core.js
Controlgroup: Heed the linter.
Unit tests: Controlgroup: Test _destroy().
Merge branch 'master' into controlgroup-widget-review
Controlgroup: Reverse the order of two if-statement branches.
testHelper: domEqual now ignores empty class attribute.
Controlgroup: Address #6163.
Unit tests: Controlgroup: Make sure options are applied correctly to pre-rendered controlgroups (issue #6163).
Merge branch 'master' into controlgroup-widget-review

Conflicts:
	js/jquery.mobile.widget.js
Controlgroup: Call refresh() when the value of the excludeInvisible option changes. Fixes #6199.
Controlgroup: Remove initSelector.
Base widget: Remove _toggleClasses.
Controlgroup: Do not call _setOptions during _create.
Merge branch 'controlgroup-widget-review'