Add initial account button with main ui header file

Also add link to UIKit.
Integrate account button into sample app

Since we're doing it without CocoaPods, the header
search paths build setting needs to be set
manually. 

And resources references need to be copied over,
since bundles can't be linked as easily as
libraries, despite much effort.
Merge branch 'refs/heads/master' into peng/add-accounts-widget
Add initial account view defines, as well as controller and its subviews
Add initial accounts manager with delegate
Add initial account model for n clients and authenticators
Add initial account model setup and accessing
Unexpose OAuth grant type constants, and delete most

Unlike AFOAuth2Client, we're only doing implicit
auth for mobile as the default auth, and password
grant type as a minority option.
Add a convenient default for token_type on the credential
Add and integrate initial draft of implicit auth flow
Merge branch 'peng/add-implicit-auth' into peng/add-accounts-widget
Tweak account's active api

Also introduce generic completion handler type.
Refine account model setup to support test tokens

Also factor out a base url helper.
Merge branch 'master' into peng/add-accounts-widget

Conflicts:
	NBClientExample/NBClientExample.xcodeproj/project.pbxproj
Introduce UIKit class extensions with alert builder
Minor client project file reorganization

In CopyFiles section.
Harden pagination info initialization
Minor authenticator cleanup and fixup
Minor defines cleanup
Minor alert builder refinement