FreeRTOS-Kernel

Added quick start guide url.

Seperated Kernel from rest of FreeRTOS code base.

Update FreeRTOS.h with the version in GitHub. This is also to test submodule.

Nordic port. Notes for Richard -- the work items we discussed about for nrf52840-dk and Wiced_CY still remain. The only reason for this commit is we want to test out submodule.

Revert 2728. Not because the files are still needed, but because we want to test out submodule.