Improve the code & documentation

• Fix ImageGen icon in CKEditor toolbar.
• Fix image dimensions display
• Review the code

Review of the 8.x-1.x branch (commit 47c473e):

    Your README.md does not follow best practices (headings need to be uppercase). See https://www.drupal.org/node/2181737 .
        The INTRODUCTION section is missing.
        The REQUIREMENTS section is missing.
        The INSTALLATION section is missing.
        The CONFIGURATION section is missing.
    Remove LICENSE.txt, it will be added by drupal.org packaging automatically.
    Coder Sniffer has found some issues with your code (please check the Drupal coding standards). See attachment.
    ESLint has found some issues with your code (please check the JavaScript coding standards). See attachment.
    No automated test cases were found, did you consider writing PHPUnit tests? This is not a requirement but encouraged for professional software development.

This automated report was generated with PAReview.sh, your friendly project application review script.


FILE: ...areviewsh/pareview_temp/src/Plugin/CKEditorPlugin/ImageGenButton.php
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FOUND 1 ERROR AFFECTING 1 LINE
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 36 | ERROR | [x] Inline comments must end in full-stops, exclamation
    |       |     marks, colons, question marks, or closing parentheses
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PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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FILE: ...b/vendor/drupal/pareviewsh/pareview_temp/src/Controller/ImageGen.php
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FOUND 1 ERROR AFFECTING 1 LINE
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 22 | ERROR | Doc comment for parameter $bg does not match actual
    |       | variable name 
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FILE: ...web/vendor/drupal/pareviewsh/pareview_temp/src/Form/ImageGenForm.php
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FOUND 2 ERRORS AFFECTING 2 LINES
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  77 | ERROR | [x] No space found before comment text; expected "//
     |       |     Assigning the config 'image_gen.config' during
     |       |     buildForm." but found "//Assigning the config
     |       |     'image_gen.config' during buildForm."
 170 | ERROR | [x] No space found before comment text; expected "// Link
     |       |     to the content of this URL." but found "//Link to the
     |       |     content of this URL."
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PHPCBF CAN FIX THE 2 MARKED SNIFF VIOLATIONS AUTOMATICALLY
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