Add changes to support MaterialDesign 5.0

[rmorgan001]

To upgrade nuget package MaterialDesignInXAML to 5.0 a few changes are needed

MaterialDesignInXAML/MaterialDesignInXamlToolkit#2255

item.IsAccented is no longer supported
Theme.Dark and Theme.Light are no longer supported.

These changes are needed in the SettingsVM.cs. Other changes maybe needed.

this may help...
MaterialDesignInXAML/MaterialDesignInXamlToolkit#2014