Move convective heat transfer coefficient and convection/radiation reference temperatures to the 'boundary' input block

[stvdwtt]

These three parameters aren't fundamental material properties and are instead depend on the environment being simulated. I think these are a better fit for the boundary input block. Normally I wouldn't say this is worth changing, but it messes with Mist integration to have non-material properties in the materials block.

Any concerns about the switch @Rombur?

h/t to @hespuck19 for catching this