Add UIView category to easily calculate CGRect for ui elements on screen (Removed Demo Project)

[fawkeswei]

With this category, you can easily get the CGRect for ui elements on screen when defining coachmarks. Also added a project to demo the usage of this category.

Usage Example

 UIButton *button = ...;
 NSArray *coachMarks = @[
         @{
             @"rect": [NSValue valueWithCGRect:[button rectToMarkInView:self.view]],
             @"caption": @"This is some awesome button!"
         }
     ];

 WSCoachMarksView *coachMarksView = [[WSCoachMarksView alloc] initWithFrame:self.view.frame coachMarks:coachMarks];
 [self.view addSubview:coachMarksView];
 [coachMarksView start];