Data models: implement schema for data

[thdrbrkw]

referencedData = {
    title*, descr, tags,
    datatype*: Referenced | NotReferenced,
    ref: {
        if Referenced {
            url*, type*, coord*
        }
        if(NotReferenced){
            {
                content, coord
            }
        }
    }
    //plus meta data fields
}

ref: ReferencedData | {content, coord}

Keys with * should be mandatory, that is:

• for referenced data URL, type and coordinates should be mandatory.
• for not referenced data, only content is mandatory, but coordinates can be added.

[Corgam]

Done with #63 .