******* ADD-ONS' IMPLEMENTATION *******
Changelist of ckeditor's files. Modified add-ons should be pasted as the are after migration:
1) /plugins/image/dialogs/image.js
Changed to use img-tag attributes instead of style properties when changing image settings in image-dialog (GWUA-2211)

2) /plugins/htmlwriter/plugin.js
Changed to keep ampersands within attributes (doesn't break href/src attributes anymore)
Changed agn-tags processing in attributes to prevent quotes escaping

3) /plugins/pastefromword/filter/default.js
Changes to trim unnecessary attributes for the `font` and remove the tag `font` if it is empty.

4) /plugins/image/plugin.js
Changes that prevent the plugin from turning img-element attributes into styles.

5) /plugins/table/plugin.js
Removed transformation of width attribute to width style. GWUA-4097

6) /plugins/showprotected/plugin.js and /plugins/showprotected/dialogs/protected.js
Implemented actual text inlining instead of icon.

7) /plugins/showprotected/plugin.js
Changed to prevent making widget of head('meta' and 'script') and comment elements.

8) /ckeditor-emm-helper.jsp
Implemented replace defaultHtmlFilterRulesForAll to prevent remove class attribute from <html> tag if fullPage is true. GWUA-4607
Introduced allowExternalScript parameter that allows external script tags

9) ckeditor.js
Fixed emoji displaying after save of data or switching to ace editor when using entities_processNumerical=true.
GWUA-4138
Before implement it please check maybe it's already fixed under the hood.
Issue link - https://github.com/ckeditor/ckeditor4/issues/4941

******* CUSTOM IMPLEMENTATION *******
EMM implementations which should also be saved after migration of ckeditor:
1) /plugins/emm/*
2) ckeditor-emm-helper.jsp
3) emm-image-browser.jsp
4) emm_config.js
5) emm_fonts.css

******* FAQ *******
In case of migration :
1) use ckeditor builder (https://ckeditor.com/cke4/builder) and upload there current version of build-config.js.
2) put modified add-ons in /plugins dir
3) put emm implementations in corresponding folders

In Case you need to modify source code of some add-on:
1) exclude you add-on from build-config.js;
2) rebuild ckeditor using build-config.js (it exclude uglified version of your add-on from ckeditor.js)
3) find and download source code of your add-on;
4) modify it;
5) include you modified add-on as external using `config.extraPlugins` property in emm_config.js file
