Remove dependencies on included layout and style option plugins from Mercury Editor

Developers / site owners should be able to uninstall Mercury Editor without any consequences to their website other than loosing the specific authoring experience enhancements offered by the module. Currently, layout and style options included in the module create hard dependencies that would prevent the module from being removed once content has been created.

Next steps:

• Remove layout plugins, style option plugins, and any other code that creates hard dependencies on the module.
• Provide an alternative solution for websites already using style options and layouts included in ME.
• Once finished, tag a new release and document the steps to remove dependencies.

Important Note about Breaking Changes:

This issue introduces breaking changes by removing all layout and style option plugins from the Mercury Editor module. For websites using Mercury Editor layout and style option plugins, developers will need to either (a) create their own alternative plugins to replace the Mercury Editor ones, or (b) download the following Drupal modules from GitHub for legacy support:

• https://github.com/AtenDesignGroup/legacy_me_style_options
• https://github.com/AtenDesignGroup/legacy_me_layouts

Finding references to layout plugins that have been removed:

Use this simple query to find references to outdated layout plugins:

select id, parent_id, parent_type from paragraphs_item_field_data where behavior_settings REGEXP '"layout_onecolumn"|"layout_twocolumn_halves"|"layout_twocolumn_onethird_twothirds"|"layout_twocolumn_twothirds_onethird"|"layout_threecolumn_thirds"|"layout_threecolumn_half_quarter_quarter"|"layout_threecolumn_quarter_half_quarter"|"layout_threecolumn_quarter_quarter_half"|"layout_fourcolumn"';

Finding references to style option plugins that have been removed:

select id, parent_id, parent_type from paragraphs_item_field_data where behavior_settings REGEXP '"display_mode"|"image_style"|"property"|"template_suggestion"';