Merge branch '15-5' into 2.5.1

[iOS] Encode url for UIWebView so it doesn't fail with non-ascii char…

…acters (xamarin#2111)

* [Controls] Add reproduction for issue xamarin#1583

* [iOS] Encode url so it doesn't fail with non-ascii characters fixes xamarin#1583

* Update Issue1583_1.cs

Revert "Disable AndroidUseLatestPlatformSdk so VS stops auto-updating…

… Android projects;"

This reverts commit 3279709.

Merge branch '15-5' into 2.5.1

Revert "Add toolbox support to nuget package (xamarin#1871)"

This reverts commit 0a2e52e.

Don't assume casts to Activity from Context will be successful (xamar…

…in#1867)

[XamlC] TypedBindings to self for value types (xamarin#1617)

fixes xamarin#1603