Search Bar: Created VectorViewController a mother class to Vector screens.

Its first feature is the management of the search bar.

Vector/ViewController/SegmentedViewController.h

@@ -16,14 +16,14 @@ limitations under the License.
 
 #import <MatrixSDK/MatrixSDK.h>
 
-#import "MXKViewController.h"
+#import "VectorViewController.h"
 
 /**
  This view controller manages several uiviewcontrollers like UISegmentedControlled manages uiTableView
  except that the managed items are custom UIViewControllers.
  It uses a Vector design.
  */
-@interface SegmentedViewController : MXKViewController
+@interface SegmentedViewController : VectorViewController
 
 #pragma mark - Class methods
 @property (weak, nonatomic) IBOutlet UIView *selectionContainer;