2.14.3 fixes

[Rarisma]

This PR does a few things in preparation for a 2.14.3 bug fix launch.

• Cleans up a bit of the webview model code and stops install failures from being reported to Elmah.io (fixes #759)
• Updates Windowing.ShowContentDialog to have logging that shows what dialog is being shown and what option was picked
• Uses null coealessing in OverviewViewModel to prevent NullRefs from occuring during saves. (fixes #755)