add checkboxes (TaskLists) to issue initial description area about eventum HOT 3 OPEN

• add to page checksum of the textarea (before changes), add the value into page form element (hidden field)
• parse body for checkboxes, add elements and number them incrementally
• when ui checkbox is clicked, ajax submit is sent which checkbox index was modified with a page checksum
• when checksum mismatches, ui displays info that page needs to be reloaded (and no checkbox change is made)

additionally to consider: do not submit change immediately. maybe user is doing two checkbox changes, it would send out two issue updated emails. delay the submit a bit (5 secs). this requires window.onunload prompt to avoid navigating off if change is yet queued. maybe visually show some circle (progressbar) that change is yet to be submitted.

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Some resources:

• https://gitlab.com/gitlab-org/gitlab-ce/blob/v11.7.5/app/models/concerns/taskable.rb
• https://github.com/github/task_list
• https://packagist.org/packages/lossendae/commonmark-task-lists

from eventum.

tasklists have been added via common mark:

• #473
• #501

now more needed is to handle UI state changes. perhaps can get help from commonmark itself:

• thephpleague/commonmark#511

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