Making the bubble images and the edge insets customizable without the need to modify the source

I added those new properties to UIBubbleTableView:
NSString *imageBubbleMine;
NSString *imageBubbleMineSelected;
NSString *imageBubbleOther;
NSString *imageBubbleOtherSelected;
UIEdgeInsets edgeInsetsMine;
UIEdgeInsets edgeInsetsOther;

By setting this a "user" of the component can set custom bubble images and also set the insets. If he doesn't set them, everything default is used just like now. So it's fully backward compatible.