Auto-configure WiFi

[rock3r]

Facility to add WiFi SSID to the device's configuration.

The goal is to allow users to configure the conference Wifi in advance (or at the venue if/when we have geofencing again, see #318). This would be likely presented with an option in the settings.

In addition to this, once this is implemented we'll prompt users in the onboarding (#60) with this feature, but it's tracked separately.

Error states: should probably just be a bottom sheet informing the user we could not setup the Wifi automagically, but that they can add it manually and give them the network name and password (with a way to copy them to the clipboard, maybe?).

Dev details

See:

• IOsched 2017's WiFiUtils
• Old Droidcon app's WiFiUtils
• ACTION_PICK_WIFI_NETWORK

[rock3r]

Done in #529 and #546 — separate action item for onboarding: #60