Initial accounts picker and flow for multiple accounts

Includes adding checks to other toggle subview
methods to only animate when needed. This is
needed because the picker view glitches when
redundant animations occur.

Also adds an error alert noting (for now) multiple
signed-in accounts per nation isn't supported.
This message is long, so alert auto-dismissal is
just removed. The flow is kept by storing the
error alert.

Note the picker rows are customized using
attributed strings. Also note the picker view
needs to be contained to be collapsible.
Remove custom account picker view subclass

There's not enough of a reason to subclass.
Re-arrange accounts view controller subviews

Move the picker closer to the account view, as it
updates according to the picker. Move the sign out
button last.
Fixup organization of accounts subviews appearance setup logic
Reset people data source when account changes
Remove deleting parent-data-source aspects from sample app

Deleting multiple people is a UI anti-pattern in
NB. The UI is wrong and should be removed. It's
also a lot of custom view-controller code.

Parent-data-source causes zombie kv-observers. Use
a delegate (new protocol) for much simpler
integration.
Merge branch 'master' into peng/add-account-switching

Conflicts:
	NBClientExample/NBClientExample/Classes/NBAppDelegate.m
Fixup close button in accounts view controller
Harden people view controller signed-in state integration

Only show decoration views if appropriate.
Account manager should try signing into first active account upon signout
Fix implicit auth callback handling in authenticator

Only adding one observer for the notification
_ever_ is a bad idea.
Keep account picker updated with data source
Harden accounts subviews visibility toggling

Keep hidden flag properly updated.
Harden when sample app's person view controller updates

Instead of logging warnings, manually wrap the calls.
Fix client sending zombie access tokens in requests
Fix zombie pagination info in sample app data source
Fix not-ready label sometimes not showing in sample app
Fix person cell de/selection in sample app

The delayed presentation of person view controller
relative to when its view gets loaded causes it to
lose its role as its navigation controller
delegate.
Fix zombie rendered UI after sign-out in sample app

The cells would blank on re-render.
Minor hardening of person view aspect in sample app