Scout/server mode locking/defaulting

[bherbst]

Support bypassing the mode select screen if desired to get scouting tablets into scouting mode more quickly. This was also intended to help prevent scouts from getting to other screens and helping them focus on scouting.

Something I'd like to avoid is that the implementation in the current (3.x) app doesn't provide any clear ways to get out of the mode and folks have gotten confused about that in the past. I think there's a balance we can provide here between keeping scouts in a more focused state (hiding server controls) while support a more explicit way to get back to a clean/default state.