Implement Android intent handling in qml app

AndroidManifest.xml register activity as an handler for retroshare links
RetroShareQmlActivity...NativeCalls.cpp bring the intent data from java
  to C++ and then to QML
QMl mainWindow uses URI.js to parse the received uri
Create a singleton for qml engine so it is reachable from NativeCalls

retroshare-qml-app/src/retroshare-qml-app.pro

@@ -4,12 +4,16 @@ QT += core network qml quick
 
 CONFIG += c++11
 
-HEADERS += libresapilocalclient.h
-SOURCES += main.cpp \
-    libresapilocalclient.cpp
+HEADERS += libresapilocalclient.h singletonqmlengine.h
+SOURCES += main.cpp libresapilocalclient.cpp
 
 RESOURCES += qml.qrc
 
+android-g++ {
+    SOURCES += NativeCalls.cpp
+    HEADERS += NativeCalls.h
+}
+
 # Additional import path used to resolve QML modules in Qt Creator's code model
 #QML_IMPORT_PATH =
 #QML2_IMPORT_PATH =