Updated Jenkinsfile & README.md

Support testing multiple on a single remote node
Updated toolversion, more concise build instructions

esp32: Fix asserts caused by mutex memory being in pSRAM.

Also implement empty() and full() methods for the Queue class.

esp32: Correct LoPy4 image script files.

esp32: Add missing Sigfox lib for the FiPy.

esp32/boards: Update flashing scripts.

esp32: Merge with master.