Change fullcalendar to a custom calendar+heatmap library/components for extended features

[cemalettin-work]

Is your feature request related to a problem? Please describe.
We would like to be able to see the engagement informations in Report Calendar + Report Statistics with a colorful heatmap to visualize clearly what is going on.
Describe the solution you'd like
I propose to create a custom library/components with features that are specific to our use cases. We can do the date-specific hard work with a library like date-fns and do the visualization + rendering with React / D3. This way, we can have more control over what custom features we can add on top.

Additional context
These slack conversations:
https://nci-agency.slack.com/archives/C67NG1BC1/p1598869587030100