Adding about page to Subsurface-mobile

This isn't pretty, but having the version string available on a place
that people are likely to find does make sense when going public with
the Subsurface-mobile. Especially when we do a public release, I assume
the developer menu with App log might not be readily available for
people to identify their installed version.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

qt-mobile/qml/main.qml

@@ -161,8 +161,14 @@ MobileComponents.ApplicationWindow {
 						manager.verboseEnabled = checked;
 					}
 				}
+			},
+			Action {
+				text: "About"
+				onTriggered: {
+					stackView.push(aboutWindow)
+					detailsWindow.endEditMode()
+				}
 			}
-
 		] // end actions
 
 		MouseArea {
@@ -240,6 +246,11 @@ MobileComponents.ApplicationWindow {
 		visible: false
 	}
 
+	About {
+		id: aboutWindow
+		visible: false
+	}
+
 	CloudCredentials {
 		id: cloudCredWindow
 		visible: false