[Ovmsdev] Transition to new esp-idf

[Stephen Casner]

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