Groups: self-management of membership of groups

- Custom the group view controllers with the blue color.

vector-im/riot-meta#114

Riot/ViewController/SegmentedViewController.h

@@ -37,6 +37,11 @@ limitations under the License.
  */
 @property (nonatomic) NSUInteger selectedIndex;
 
+/**
+ The tint color for the section header (kRiotColorGreen by default).
+ */
+@property (nonatomic) UIColor *sectionHeaderTintColor;
+
 /**
  The view controller that currently has the focus.
  */