Refactor App Data Exposure

[synthfi]

Current system relies on MessagePack for data exposure, which works well but bloats each app compiled size and excludes Fortran due to it not having an available MessagePack implementation.

Priorities:

• Maintain POD capability
• Strings
• Vector Strings

Option 1. Pointers

• no vector of strings
• easy

Option 2. JSON

• more extensible
• fortran support