New Milestones Feature

[zazzcode]

My idea is to create a new milestone feature that will use a Gantt chart ui component to allow a user to create milestones and associate deliverables with milestones. This should be linked to the status of the deliverable to see when started and completed and automatically update the bar on the Gantt chart.

We should be able to also plan a start date (when needs ot start) and lay out a sequence of deliverable based on their dependencies

The milestone will have a date / calendar across the top and a tree view of milestones and child deliverables on the left. Will create the MVP using this library and see if it is sufficient or if we need to fork and customize:

https://github.com/svar-widgets/react-gantt