Added ShortcutActivity class to respond to homescreen shortcut intent.
It will show file dialog and return path to selected file as intent response.
Added simple file chooser dialog,
This is to select game iso when creating homescreen shortcut.

Probably not an ideal solution, could use ppsspp internal GameBrowser later.
Added name to display when user long-press homescreen and choose "Shortcuts".
In our case it's "PPSSPP game".
Added ShortcutActivity class on ppsspp manifest, so it will appears on homescreen shortcuts choice ("PPSSPP game" in our case).
- Moved SHORTCUT_EXTRA_KEY and shortcut query here.

- Call super.setShortcutParam(getIntent().getStringExtra(SHORTCUT_EXTRA_KEY))
before super.onCreate()
- Change SHORTCUT_EXTRA_KEY reference from NativeActivity to PpssppActivity.