Threat model file format

[jgadsden]

The file format used in Threat Dragon versions 1.x and 2.x are incompatible with other open source Threat Modeling files such as pytm, Threagile and Open Threat Model.
It would be good to define a schema that is flexible enough to easily convert from the existing:

• [OWASP Threat Dragon] versions 1.x and 2.x
• [OWASP pytm][pytm] pythonic threat modeling
• [Threagile][threagile]
• [Open Threat Model][otm] (OTM)