[Ovmsdev] Transition to new esp-idf

We expect production OVMS to be based on release/v3.1 of esp-idf in order to incorporate the support for SPIRAM (PSRAM).

I'd like to set a target for all develpers to move to the master branch of openvehicles/esp-idf that contains the finished version of my modifications to support the "module memory" command. At the same time I need to then merge the corresponding changes from my temporary branch in openvehicles/Open-Vehicle-Monitoring-System-3 to the master branch there since the API between the two has changed.

In other words, we need a flag day.

                                                    -- Steve