Replies' privacy scope should not be higher than original post

[ShadowJonathan]

In conjunction with #232

Have it so a "followers-only" post cant be replied with (by default) with a globally-scoped message, but instead it also defaults to followers-only.

Same with unlisted, and DMs (like the issue above)

[MainasuK]

The app should set visibility not higher than replied post in v1.0.1 (51) now.

[whattherestimefor]

Reported: When replying to an unlisted post, the composer defaults to public, not unlisted.