Update CKEditor library to 4.7.1

When building CKEditor 4.7.1, I noticed that it grew from 563 KB for 4.6.2 to 576 KB for 4.7.1. I asked the CKEditor team for an explanation.

The new Advanced table selection actually is a new optional plugin: https://ckeditor.com/addon/tableselection. It's 31 KB, which is quite a lot. So, for now, not adding this to our CKEditor build. It'll make CKEditor slower for everyone, even though only a minority uses the "Table" tool in CKEditor. Besides, these updates are meant to be just updates, not adding more plugins.

IS updated.

improved conformance with Content Security Policy was one of the highlights of CKEditor 4.7. What does this mean exactly?

CKEditor 4.7 brings improved compliance with CSP with the removal of dynamic evaluation calls in the template system. Thanks to this, the editor can now be used with unsafe-eval Content Security Policy.

Source: http://ckeditor.com/blog/CKEditor-4.7-released

Therefore this closes #2789139: [upstream] CSP requires 'unsafe-inline' because of CKEditor 4 and helps #2513356: Add a default Content-Security-Policy and clickjacking defence to core.

The new Mexican Spanish localization (es-mx) is one that Drupal does not have.

See https://localize.drupal.org/.

The infrastructure for making CKEditor use the same language as Drupal core was added in #2050097: Map CKEditor languages to Drupal languages. And even then, there were some localizations that CKEditor has that Drupal doesn't, for example en-au.

This then follows the example set there: we still add this language, so that sites that add es-mx themselves, then they'd get that translation in CKEditor too.

Only two noteworthy things in this patch:

1. added two ignore lines to build-config.js, which have been added upstream (to prevent bender.ci.js and .travis.yml from making it into Drupal core)
2. added es-mx translation
3. updated versions in core.libraries.yml

I did manual testing, it still works fine.

#9: is it possible you had the ckeditor_test module installed during your testing? The purpose of that module is testing hook_ckeditor_css_alter(), which is indeed adding that file.