This commit refactors port_common.c so that it only contains implementation of
FreeRTOS port functions that are common to all FreeRTOS ports (i.e., on all
architectures and on all FreeRTOS implementations).
* Added port layer from the FreeRTOS POSIX port, added
additional port code for ESP-IDF.
* Created another hello world example using that POSIX
port in tools/test_apps.
* Removed old linux app