Android: Make build system for apps

We need a build system for apps based on qmake or QBS which does not require Qt Creator for making Android apps. (android_app.prf or something like that can be used for this, which could possibly be set by default for application builds?)

It should:

1. Allow you to specify the AndroidManifest.xml file to use, and then copy this into a build directory. Use the default from Qt if not specified.

2. Allow you to specify the QtActivity.java and QtApplication.java to use and copy this into a build directory. Use the default from Qt if not specified.

3. Generate a libs.xml somehow and the other things required for deploying the app.

4. Copy the library into build_dir/libs/<arch> after building.

5. Copy QML files and other required files into the assets folder of the apk (similar special rules as meego deployment of QML)

6. Make assets folder a default search path for QML files on Android.

7. If possible, make a build system for the steps currently performed by ant. If it is required that this adapts to new Android SDKs as they come out and therefore needs to use the default Android build script, then we should copy the build.xml from Qt into the build directory and document that you should do the ant step manually in the case where you're not using Qt Creator for building.

Goal should be that examples build deployable .apks with no or few modifications to the .pro files. Qt Creator should be updated to support this system when it's done. This has the benefit that we don't generate files into the project that are maintained partially by Qt Creator and partially by the user, and we never overwrite QtActivity.java if people want to use a custom one.