Fix view not updating when Model is changed.
Fix view not updating when Model is changed.

Consider the following binding

```
plotView.SetBinding(PlotView.ModelProperty, "PlotModel");
```

This updates the model when the property is changed in the ViewModel. However these changes are not reflected in the View. When adding `SetNeedsLayout` after the Model is set in the code. The changes now reflects in the UI.
jeremyiverson/oxyplot,HermanEldering/oxyplot,freudenthal/oxyplot,olegtarasov/oxyplot,H2ONaCl/oxyplot,GeertvanHorrik/oxyplot,DotNetDoctor/oxyplot,lynxkor/oxyplot,objorke/oxyplot,svendu/oxyplot,bbqchickenrobot/oxyplot,objorke/oxyplot,bbqchickenrobot/oxyplot,Rustemt/oxyplot,H2ONaCl/oxyplot,objorke/oxyplot,HermanEldering/oxyplot,Sbosanquet/oxyplot,jeremyiverson/oxyplot,freudenthal/oxyplot,NilesDavis/oxyplot,Mitch-Connor/oxyplot,mattleibow/oxyplot,lynxkor/oxyplot,svendu/oxyplot,as-zhuravlev/oxyplot_wpf_fork,ze-pequeno/oxyplot,Mitch-Connor/oxyplot,sevoku/oxyplot,Sbosanquet/oxyplot,as-zhuravlev/oxyplot_wpf_fork,Isolocis/oxyplot,zur003/oxyplot,freudenthal/oxyplot,BRER-TECH/oxyplot,shoelzer/oxyplot,olegtarasov/oxyplot,Kaplas80/oxyplot,sevoku/oxyplot,Rustemt/oxyplot,Rustemt/oxyplot,mattleibow/oxyplot,TheAlmightyBob/oxyplot,shoelzer/oxyplot,br111an/oxyplot,Jonarw/oxyplot,br111an/oxyplot,GeertvanHorrik/oxyplot,shoelzer/oxyplot,TheAlmightyBob/oxyplot,Jofta/oxyplot,Mitch-Connor/oxyplot,GeertvanHorrik/oxyplot,BRER-TECH/oxyplot,as-zhuravlev/oxyplot_wpf_fork,Sbosanquet/oxyplot,jeremyiverson/oxyplot,H2ONaCl/oxyplot,br111an/oxyplot,DotNetDoctor/oxyplot,TheAlmightyBob/oxyplot,svendu/oxyplot,oxyplot/oxyplot,Kaplas80/oxyplot,bbqchickenrobot/oxyplot,lynxkor/oxyplot