Concurrent task editing

We have a small team that uses task description to document task progress and other task related topics. Because there is no built-in resolution of concurrent editing, users regularly loose their changes while editing the same task.

Because Kanboard is primarily intended to be a collaborative tool, I think the prevention or resolution of editing conflicts should be a core feature.

In a minimal implementation, the task editor should block the simultaneous editing of the task or at least show a clear warning that another user is currently editing the same task.

A more advanced implementation could attempt to resolve the conflict with the help of the user, who decides which changes are merged and how.

The most advanced solution would be to implement a collaborative real-time editor like ProseMirror :grin:

Related GitHub issue: #944

We perform a similar function using the Comments functions of the Tasks. This also provides traceability of the comment back to the user. The Comments Tool Tip plugin provides a nice hover-style pop-up for the comments on tasks, also.