TemplatePicker based on SymbolDisplay:

  - TemplateItem (private class but used for Binding):
      . Removed Swatch Property
      . Added GeometryType and Symbol properties
  - Default template picker styles based on  SymbolDisplay
  - Use Loaded/Unloaded events to subscribe/unsubscribe to layers events
Merge branch 'dom/issue57_SymbolDisplay' into dom/TemplatePicker_UseSymbolDisplay
Updated due to SymbolDisplay namespace change.
Remove dependency properties SwatchDpi, DefaultWidth and DefaultHeight
Merge branch 'dom/issue57_SymbolDisplay' into dom/TemplatePicker_UseSymbolDisplay

Conflicts:
	src/Common/Esri.ArcGISRuntime.Toolkit/Controls/TemplatePicker/TemplatePicker.cs
Merge branch 'v.next' into dom/TemplatePicker_UseSymbolDisplay

Conflicts:
	src/Common/Esri.ArcGISRuntime.Toolkit/Controls/TemplatePicker/TemplatePicker.cs
Merge branch 'v.next' into dom/TemplatePicker_UseSymbolDisplay
Merge pull request #80 from Esri/dom/TemplatePicker_UseSymbolDisplay

TemplatePicker based on SymbolDisplay