Fragment Shader Output Semantic

Allow us to specify which fragment shader output semantic we would like to use (or choose automatically based on our selected platforms). It seems that all shaders created in Shader Forge use the COLOR semantic, but some platforms require this to be SV_Target instead (PS4, for example).
Similarly, PS4 requires the use of the SV_Depth semantic on fragment shader output instead of DEPTH, though I haven't made any shaders that would output depth, so I don't know how Shader Forge currently handles this.