Add WYSIWYG for story page content

[ctwhome]

User story

As an editor
I want to edit my stories with a WYSIWYG editor

Proposed work

• Use CKEditor or similar

##Progress

• Managed to integrate ckeditor with react component
• Able to get the changed content from editor
• changes are pushed into feature/ckeditor branch

TODO

• to enable image upload needs to add upload adapter & make some server side configuration
  https://ckeditor.com/docs/ckeditor5/latest/features/image-upload/image-upload.html
  https://stackoverflow.com/questions/46765197/how-to-enable-image-upload-support-in-ckeditor-5

• In order to save content to database scenarios needs to be added
  in api for updatePage there is scenarios object which needs to be passed & content is part of scenarios

scenarios {
        id
        ssp
        content
        split_map
        enabled_catalog_items {
          id
          json
        }
      }

Acceptance Criteria

• Update documentation

Designs

[kretep]

@pushpanjalip Uploading images now works. Progress is in https://github.com/RECEIPT-H2020/terriajs/tree/feature/ckeditor

I guess the next step would be to actually save the ckeditor content and reloading it.