Cascading updates of milestones and timeline when deleting a milestone

[maxceem]

Currently, we are making a lot of cascading updates of milestone when we update milestones. But we also have to do similar cascading updates when we delete a milestone, as it can cause changing other milestones start/end dates. And start/end date for the whole timeline.

Here is a related issue about cascading updates on milestones adding #378

[maxceem]

I think we can skip this issue for now, as we are going to reformat the format of milestones to points, and we wouldn't have such functionality, see the related issue appirio-tech/connect-app#3299.

[vikasrohit]

Moving to backlog for now following #378 (comment)