With an upcoming bok-choy upgrade, 'not-present' and
'invisible' are two distinct concepts. In the upgrade, an
invisible element must be present on the page. This commit
draws that distinction across two helper methods, one for
'invisible' and the other for 'not-present' (or, not on the page at all).
TE-849
This passes fine in firefox; however in chrome, the click is occurring before
the page is ready; and then the click itself is not specific enough. Also
refactored the add button method so it more-clearly returns the expected
end-state.
