Merge pull request #37 from brunchboy/emptyPrompt

Support empty prompts, have the prompt cell take up no space when...
Working implementation of optional prompt cell.  Needs refactoring to consolidate the indexing logic.
Add showPrompt property to both MBContactPicker and MBContactCollectionView, default both to YES
Code formatting for demo view controller
Only refresh the prompt cell when showPrompt is toggled in the MBContactCollectionView.  This provides a nicer user experience where cell highlight state is maintained and an animation is used for the addition/removal of the prompt.
If we have to use a magic constant, lets at least put it in one place.
Prompt cell required width calculation wasn’t taking the UILabel’s font into account so it wasn’t growing wide enough.  Fix.
Get rid of automatic collection view reload when changing prompt settings at the MBContactPicker level
Remove code that was resizing the prompt cell to a very small size.
Formatting of -[MBContactPicker setup] method
Update readme.md with prompt changes
Prevent index 0,0 reloading when the prompt text is updated if the prompt isn’t currently displayed (0,0 would be occupied by a contact cell in that case).
Merge pull request #45 from Citrrus/feature/optional_prompt_cell

Feature/optional prompt cell
Support a localizable version of the prompt text with a safe default value
Add prompt text i18n details to readme.md
Merge pull request #46 from Citrrus/feature/nslocalizedstringsupport

Feature/nslocalizedstringsupport
Make MBContactPickerModelProtocol properties read-only, since that is all
that the picker implementation requires, and avoids implementors having to
either provide setters, or ignore the Xcode warnings about them not being
auto-generated.
Fix bugs related to setting MBContactCollectionView.prompt or MBContactCollectionView.showPrompt before a -[UICollectionView reloadData] has been invoked (either explicitly or implicitly).
whitespace
Merge pull request #50 from Citrrus/feature/fix_#48

Feature/fix #48