Don't forcibly push the user to SettingsActivity from MainActivity

[Cliabhach]

MainActivity::loadPreferences, when we don't have an IP address, automatically opens the settings screen (SettingsActivity). This means that if the user opens this app for the first time, they will be immediately pushed to SettingsActivity.

It also means that pressing back from SettingsActivity without having a valid stored IP address may cause this code to run, pushing the user forward into SettingsActivity. This occurs naturally on low-memory devices, and can be easily simulated by enabling the developer option Don't keep activities.

I suggest that we instead put a noticeable (but non-modal!) warning that the app is not fully configured, with a button to view app settings. Perhaps a SnackBar?

[Cliabhach]

May be linked to issue #54

[seymour-bootay]

Lets disscuss this after i get my changes in. I am still forcing to settings but there is better feedback on the screen when the app is not configured.