Improve error reporting: Extract original message when showing "Java exception messages" consistently. Improve error handling in deprecated OneDrive API stub and avoid crash by no-longer throwing in Main-thread methods.

src/keepass2android-app/GeneratePasswordActivity.cs

@@ -543,7 +543,7 @@ namespace keepass2android
             }
             catch (Exception e) 
             {
-				App.Kp2a.ShowMessage(this, e.Message,  MessageSeverity.Error);
+				App.Kp2a.ShowMessage(this, Util.GetErrorMessage(e),  MessageSeverity.Error);
 			}
 			
 			return password;