* This installer is invoked when for non-apk/media files, and
copies them to an appropriate folder on the sdcard.
* We also introduce a FileInstallerActivity to ask for storage
permissions at runtime, as needed by Android 6.0 and above,
and handle the install/uninstall process.
* A toast is shown with the install path after installation.
TODO:
* Manage Installed Apps screen doesn't show media files.
