Add seleniumable element classes/ids.

[mcav]

As noted in #19, we don't have any useful selectors for testing. This is largely due to styled-components, which hashes CSS class names for various reasons. We should add class names, or maybe just IDs, to all user-touchable components, so that we can write tests without going batshit crazy. :)

[isabelrios]

Thanks for the explanation! So far it is not difficult to find the xpath or css selector for each element, the problem is that they do not look nice and the tests need a lot of maintenance as the xpath/selector changes while developing the website.
#19 has been closed since a new version of the tests is being developed following the PO pattern.
That new version will have temporary selectors till having the class names or ids, it would be easier to change to the final ones since the selectors are defined in one place, but at least in the meantime will allow QA to work on the skeleton and coverage of the tests.
Thanks!