WIP: add query methods

[generalov]

PR to extend find with additional query methods:

.before((actions, find) => {
  actions.click(find(".link")) 
  actions.click(find.link("Click Me"))
})

• [x] css
• [x] link
• [x] xpath
• [ ] a11y (https://github.com/admc/wd/blob/master/doc/api.md)

Supersedes #896