Documentation

[akabishau]

this PR adds new functionality to the core project that will be used as building blocks for the documentation:

• mapping: dynamically built table that represents current mapping state of the table; the logic includes snapshot functionality to support tracking of changes
• metadata: table captures current state of the ctgov study model; supports snapshots but currently uses static json file to as a source of information
• schema: table represents current state of available "ctgov" schema table and columns; supports snapshots to keep track of historical changes