Added Schema for JSON

Added

• Added TDVisu.schema.json to validate the Json-API for TDVisu [#24]
• Added 'col' to allowed formats in tw reader (default string in Mathematica)

Changed

• Fixed error where database configuration was not found in the directory
• Fixed missing double quotation marks in JsonAPI.md
• Moved JsonAPI.md → doc/JsonAPI.md

Removed

• Removed generalGraph and incidenceGraph from required arguments in API