Adding the scroll_to_collection_view_item_with_mark method on client
side to complete the pull request #36
Added rdoc comments for the scroll_to_row_with_mark and
scroll_to_collection_view_item_with_mark methods.

Also changed the "row_id" / "item_id" var name to "mark", and removed
unnecessary checks on options as recommended by jmoody.
bumped version to 0.9.168.pre2 and updated the changelog

also changed a screenshot_and_raise to raise because the assertion is
on the arguments not on the state of the app.