variant of github/leah PullRefreshTableViewController w/plain UIVC as base

it's often necessary to embed UITableView's in plain UIViewControllers,
since it's often necessary to hang UI around the edge of the table that
shouldn't scroll with the table.  so, this version, called PullToRefresh
to slightly distinguish it, is derived only from UIViewController, but
conveniently includes it's own @property tableView and declares this thing
a UITableViewDataSource and UITableViewDelegate, so subclasses can act
pretty much as they are used to doing if subclassing from UITableViewController