Showcase APK fusing in the sample

[pfmaggi]

Given that Splits have been introduced in API Level 21, when Play delivers an Android App Bundle to a device running KitKat or older OS it implements APK Fusing as explained at step 6.c. of the dynamic features module docs.

Would be helpful to show in this sample how to gracefully allow an application, using dynamic features module, to target API Level 19 and lower using the fusing directive:

<dist:module
    ...
    <dist:fusing dist:include="true" />
</dist:module>