panic app and repo wipe

This extends the panic "destructive" response options based on the setup from !629 (merged). It adds two new possibilities for responses:

• reset the whole repo setup to default, e.g. deleting any extra repos
• uninstalling a user-configured list of apps (requires Privileged Extension)

This will be really awesome in conjunction with: https://gitlab.com/calyxos/calyxos/issues/72

@grote @cde @jefflandale @nickcalyx

Here's an upcoming blog post with a bit more info, I'll edit a version for f-droid.org also: https://eighthave.gitlab.io/info/2019/06/04/panickit-1.0-built-in-panic-button-and-full-app-wipes/