Mindjet example style.
Make placeholder color part of A0Theme.
Theme improvements.

Now it possible to customize:
* field placeholder color
* activity indicator color
* status bar style
Style activity indicators.
Image as bg of A0LockViewController.
Theme in SMS & TouchID.
Change theme from settings in Lock app.
Merge pull request #60 from auth0/chore-example-theme

Theming improvements & Example Theme