Handle clipboard history properly

[cole-h]

Some systems store clipboard history, so we should probably clear/overwrite it; right now, we do nothing. Examples of how pass and gopass achieve this are below (seems to just be through a dbus connection).

https://git.zx2c4.com/password-store/tree/src/password-store.sh?id=88936b11aff49e48f79842e4628c55620e0ad736#n184

https://github.com/gopasspw/gopass/blob/beb22bc1052457c24410e263c7517ab0036a51cc/pkg/clipboard/unclip_linux.go#L12