High impact for 2019.10

PRs that likely have a high impact on RIOT as a system.

cpu/esp32/esp wifi: add WPA2 enterprise mode with IEEE 802.1x/EAP authentication (#12024)

pkg/tinydtls: add DTLS sock API implementation (#11943)

kinetis: Implement low power modes (#11789)

sock: initial definitions for asynchronous event handling (#11723)

makefiles: introduce 'LIBS' variable (#11111)

usbus: Add CDC-ACM (Serial console) function (#11085)

gnrc_lorawan: add initial support for GNRC based LoRaWAN stack (v2) (#11022)

riotnode: node abstraction package (#10949)

Still WIP, so doubtful this will get in

??? sys/shell: add heap command (#10953)

Has been tested quite a bit, but @MrKevinWeiss asked for a hardware test

??? sys/arduino: Added Wire (I2C) interface (#10592)