Add knowledge base statistics dashboard

[isaisabel]

As a user of the ATT&CK Workbench, I want to be able to do basic analysis of the contents of the knowledge base using a visualization dashboard. I also want to use this dashboard to assess the workflow states as part of my quality control process.

• I want to be able to use a sunburst diagram to assess the number of objects in a given workflow state by object type, by domain. For example, to drill down from Enterprise -> techniques -> # WIP.
• I want to be able to use a percent stacked area graph to assess how the workflow states of my knowledge base have evolved over time.
• I want to be able to use a line plot to assess how the number of objects of each type has changed over time. I want to be able to optionally filter this to only include one domain at a time.