adds LPScrollToRowWithMarkOperation which allows calabash-cucumber to
send queries using :scrollToRowWithMark.  this allows testers to
scroll to a row using a mark instead of using an index (path).

supports searching for cells by:

* accessibilityIdentifier (iOS 5+)
* accessibilityLabel
* subviews in the cell's contentView that match:
** accessibilityIdentifier (iOS 5+)
** accessibilityLabel
** text (UILabel and UITextView)

for more details see:

* calabash/calabash-ios#128 for more details
* https://github.com/calabash/calabash-ios-server/pull/17
Merge pull request #18 from jmoody/0.9-scroll-to-row-marked

adds support for scroll to rows in table view by mark (access id, access label, and text)