Add includes polyfill for IE11

[Yago]

Add the following Polyfill for String.includes :

if ( !String.prototype.includes ) {
  String.prototype.includes = function(search, start) {
    'use strict';
    if (typeof start !== 'number') {
      start = 0;
    } 

    if (start + search.length > this.length) {
      return false;
    } else {
      return this.indexOf(search,start) !== -1;
    }
  };
}

[Yago]

should be fixed with frontend/toolbox-utils@0ba0607

[gido]

For some reason this is not enough for IE 11 / Windows 8.1 (Browserstack):

The polyfill doen't look to be served by polyfill.io
/cc @zufrieden

[gido]

Or maybe we are calling includes on something other than a String...

[dmrty]

Correct @gido, Array.prototype.includes is needed as well.
Used at least at the following locations :

• src/views/Doc/Doc.js

<script src="https://cdn.polyfill.io/v2/polyfill.js?features=String.prototype.includes,Array.prototype.includes,Array.prototype.find"></script>

solves the problem.

[dmrty]

Also needs to update the doc accordingly.