Bug fixes and new widgets

Fixed bug in BaseWidget that makes widgets without input throw an exception.
Now checkboxes are positioned left relative to the label as anyone would expect.
Fixed a couple of bugs in checkboxes.
Added radio buttons.
Theme switcher now uses radio buttons instead of drop-down menu.
Added buttons and group of buttons.
Added ItemsWidgetInterface for implementing widgets that can have multiple items. Drop-down lists, radio buttons and buttons groups implement this interface.
Now widgets can specify container for revert button added by the settings.
Fixed wrong layer menu height. Unfortunately, it causes broken animations in old Chrome, so menu now won't be animated in such Chrome versions.
Fixed wrong L.ALS.Helpers.makeHideable() behavior.
Fixed drop-down menus in old browsers.
Fixed layer type menu in wizard window.
Changed the way mobile icons are being applied.
Made wizard labels less verbose.
Removed unnecessary comments from drop-down lists and radio buttons.
Removed outdated TODOs.