Added support for customizing an indicator view. Defaults to the stan…

[sveinhal]

…dard typingIndicatorView

By calling -registerClassForIndicatorView: during initialization of the view controller, you can customize the appearance and behavior of the typing indicator view.

If not called, or a subclass of SLKTypingIndicatorView is passed, -typingIndicatorView will return the typing indicator view as before. If some other subclass of UIView is passed, -typingIndicatorView will return nil, and you need to cast the return value of -indicatorView to the appropriate type in you need to interact with it directly. Setting its hidden property to either true or false, will automatically animate.

This closes #201

[sveinhal]

This makes the examples work with no modification and should assure backwards compatibility. However, since the indicator view is instantiated by the view controller, and can be any UIView subclass, a consumer must have to cast the return value of indicatorView to the appropriate type. This is perhaps not optimal:

@interface MyTextViewController: SLKTextViewController
@property (nonatomic, readonly) MyTypingIndicatorView *indicatorView;
@end

@implementation MyTextViewController
@dynamic indicatorView;
- (instancetype)init {
    self = [super initWithTableViewStyle:UITableViewStylePlain];
    if (self) {
        [self registerClassForIndicatorView:[MyTypingIndicatorView class]];
    }
    return self;
}
@end

[sveinhal]

This also gets away with no particular protocol or subclass, since the view controller is using KVO to listen for changes to the hidden property, and adjust the height accordingly.

[dzenbot]

I will have a look on this real soon! Thanks!

[sveinhal]

@dzenbot Do you have time for a look at this?