fix Update function
handle visibility from associated owner for all glow windows
update clean and flyout example with hide/show
OnlyLoadTransition for MetroContentControl

this is used by MetroWindow and CleanWindow to avoid running the
transition twice, if hidden window is shown again
use VirtualisedMetroListView in flyout example
Merge pull request #843 from MahApps/839-punker76-trouble-with-glowbrush

fix the trouble with glowbrush when Window hide/show