KxSMBSample improvements

Alert view added to specify host.
Button to connect to other host.
Last server used is saved in the user preferences and autocompleted
when the app is loaded.
Back buttons now shows only the folder name instead of the full path.
TreeViewController is now a UITableViewController.
Refresh control added.
TreeViewController updates file list on path change.
Head TreeVC is now reloaded when the authentication has been done.
Image preview in FileViewController.