Fixes #485
Needs to wait until the control is loaded before setting banner text.
When the ItemsSource has changed, reset the SelectedIndex to 0.
Made sure SelectedIndex was 0 when the FlipView's template is applied.

Signed-off-by: Amrykid <amrykid@gmail.com>
FlipView accepts the Left and Right arrow keys for going Backward and Forward respectively.
FlipView's inner controls can now longer receive tab focus.
Uses GetTemplateChild instead of Template.FindName. Added Show/Hide Controls methods.
Fixed flicker of FlipView's banner text when the banner's enabled status is toggled.
Fixed a bug where the FlipView was unloaded by the TabControl but it's inner events weren't reattached when the Tabitem was switched back.
Fixed some 'Warnings'.
Merge pull request #486 from Amrykid/flipview-patch1

FlipView Patch #1