Add support for required attribute to form plugin.
Removed obsolete vertical-align style set on several fields' containers in Select dialog.
Tests: Updated tests of Checkbox, Textarea and Textfield dialogs.
Tests: Added tests of Radio and Select dialogs.
Tests: Fixed code-style of various Forms tests.
Tests: Added test for empty fields in Textarea dialog.
Tests: Improved several Forms tests to check if field values are loaded properly.
Tests: Fixed broken Select test in IE.
Tests: Ignored several Radio tests in IE as the feature appears broken in that browser family.
Changelog entry.
Merge branch 't/11583' into major