Docs: Add condensed cheat sheet.

[cvakiitho]

Heavily inspired by:

https://gist.github.com/javierarques/0c4c817d6c77b0877fda

[philipphoberg]

Very useful, thanks!
Regarding the clear() function:
I noticed that some ui5 inputs are not effected by element.clear(). It seems to be some kind of Webdriver issue. (clear() will not take effect if the autocomplete attribute of the target element is 'off' or 'on')
Maybe my workaround is worth an addition to the cheatsheet.

let clear = element => {
  element.getAttribute('autocomplete').then(value => {
    if (value !== 'none') {
      element.getAttribute('value').then(value => {
        let backspace = protractor.Key.BACK_SPACE;
        element.sendKeys(backspace.repeat(value.length));
      });
    } else element.clear();
  });
}; 

[maximnaidenov]

Hi Phillip, thanks for sharing this tip. I will try to work on the guide (remove some practices that I consider dangerous) and merge it very soon, and then I will merge this tip also.

[CLAassistant]

All committers have signed the CLA.