Expose titleLabel and subtitleLabel

[yimingtang]

Hey Sam, I am wondering if it is a good idea that we expose the titleLabel and subtileLabel properties in SVPullToRefreshView.

I'd like to do some custom configurations on such kinds of labels, but I don't want to modify code in your library. You know, I may use pull-to-refresh in many situations and they look little different.

[samvermette]

Yeah I think this is a good idea. Can you submit a pull request? Make sure they're exposed as readonly attributes though.