Components should calculate minWidth and minHeight when measuring

[joshtynjala]

Defaulting to 0 results in an issue with percentage dimensions, if the parent container doesn't have a width or height.

• [x] Alert
• [x] AutoComplete
• [x] Button
• [x] ButtonGroup
• [x] Callout
• [x] Check
• [x] DateTimeSpinner
• [x] Drawers
• [x] GroupedList
• [x] Header
• [x] ImageLoader
• [x] Label
• [x] LayoutGroup
• [x] List
• [x] NumericStepper
• [x] PageIndicator
• [x] Panel
• [x] PanelScreen
• [x] PickerList
• [x] ProgressBar
• [x] Radio
• [x] Screen
• [x] ScreenNavigator
• [x] ScrollBar
• [x] ScrollContainer
• [x] Scroller
• [x] ScrollScreen
• [x] ScrollText
• [x] SimpleScrollBar
• [x] Slider
• [x] SpinnerList
• [x] StackScreenNavigator
• [x] TabBar
• [x] TextArea
• [x] TextCallout
• [x] TextInput
• [x] ToggleButton
• [x] ToggleSwitch
• [x] WebView
• [x] DefaultListItemRenderer
• [x] DefaultGroupedListItemRenderer
• [x] DefaultGroupedListHeaderOrFooterRenderer
• [x] TextFieldTextRenderer
• [x] TextFieldTextEditor
• [x] StageTextTextEditor
• [x] TextBlockTextRenderer
• [x] BitmapFontTextRenderer

[joshtynjala]

This should be 3.0 because it's likely to break some legacy code, as it effects a number of core components that want to use _minWidth and _minHeight variables that are going to be removed.