Return full code reply via HTTP rr_reply code for corresponding rr_gcode calls

[chrishamm]

@T3P3 requested a better rr_reply HTTP interface which returns the matching G-code reply of a previously issued rr_gcode request. At the moment DWC replies can be duplicated (and logged multiple times, e.g. in a macro when dealing with M291/M292 and echo calls) which makes code reply parsing in plugins more difficult and has the potential to confuse users.

Possibly rr_gcode could return the next sequence number and rr_reply could accept that previously returned sequence number to return only a subset of the buffered G-code reply. M122 and other codes that do subsequent Platform::Message(F) would need special handling, though.