Interface semantics

[Kronos3]

Implements the semantics of FPP Interfaces

• I pulled out common port maps/checking interface GenericPortInterface so that Interface and Component would not have duplicated code.
• I had to rework the C++ header computation a bit since interfaces are not a code-generated symbol like our other symbols. Rather they are compile-time only and refer to other symbols.

Closes #699

[Kronos3]

@bocchino I've gone through https://github.com/nasa/fpp/wiki/Adding-New-Features-to-FPP#tools and updated tests accordingly. I'm not quite sure about the changes to the fpp-to-json outputs since there is a new field that is added to import.

Is there a JSON schema I need to update for the fpp-to-json output or is that just for the dictionary?

[bocchino]

Looks good!

[bocchino]

Is there a JSON schema I need to update for the fpp-to-json output or is that just for the dictionary?

There is no schema for the fpp-to-json output. Most of it is auto-generated by circe.