Added detection of touch devices before first touch events happen on Android.

On Android available touch devices are now added with video initialization (like
the keyboard). This fixes SDL_GetNumTouchDevices() returning 0 before any touch
events happened although there is a touch screen available. The adding of touch
devices after a touch event was received is still active to allow connecting
devices later (if this is possible) and to provide a fallback if the new init
did not work somehow. For the implementation JNI was used and API level 9 is
required. There seems to be nothing in the Android NDK's input header (input.h)
to implement everything on C side without communication with Java side.

src/video/android/SDL_androidvideo.c

@@ -36,6 +36,7 @@
 #include "SDL_androidclipboard.h"
 #include "SDL_androidevents.h"
 #include "SDL_androidkeyboard.h"
+#include "SDL_androidtouch.h"
 #include "SDL_androidwindow.h"
 
 #define ANDROID_VID_DRIVER_NAME "Android"
@@ -165,6 +166,8 @@ Android_VideoInit(_THIS)
 
     Android_InitKeyboard();
 
+    Android_InitTouch();
+
     /* We're done! */
     return 0;
 }