Adds regex for time duration to result subschema
Adds context subschema and integrates it in statement schema
Extends context subschema. Adds Activity subschema and Object subschema without substatements
Renames xAPI.json to Statement.json
Implements substatements as objects and sets new entry schema to xAPIStatement.json
Removes unnecessary files
Adds description to json-schema files if missing
Extends context subschema with contextActivties and fixes a bug in activity subschema