Add support for non-apk files
Introduce FileInstaller, a way to handle media files from F-Droid
- 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.
- Manage Installed Apps screen doesn't show media files. This can be done later, by either adding the media files to the current installed apps screen, or creating a new screen.
Also includes: AppProvider: Use IS instead of = for suggestedApk calculation
- For non apk files, the signature column would be NULL always, and in SQLite NULL = NULL is false, but NULL IS NULL is true.
See http://www.sqlite.org/lang_expr.html Operators
Closes #1023 (closed)