updates for Feathers 1.2 beta
link to beta docs in the readme
examples build tweak
TextFieldTextRenderer: added disabledTextFormat (closes #266)
Themes: support for disabledTextFormat on TextFieldTextRenderer
ComponentsExplorer: tweak to some text
ListCollection: return from removeAll() if length == 0
List, GroupedList: support for item renderers that can be deselected if multiple selection isn't enabled
DefaultListItemRenderer: better management of isToggle for multiple selection to allow list.itemRendererProperties.isToggle to be set manually on single selection
Item renderers: fix for measurement when label is missing
added missing notes about beta components