* BIG refactor: 'board' and 'radio' objects now defined in 'target.h/.cpp'

* mesh::RTCClock class moved to MeshCore.h

variants/heltec_v2/platformio.ini

@@ -3,6 +3,7 @@ extends = esp32_base
 board = heltec_wifi_lora_32_V2   ; heltec_wifi_lora_32_V2
 build_flags =
   ${esp32_base.build_flags}
+  -I variants/heltec_v2
   -D HELTEC_LORA_V2
   -D PIN_BOARD_SDA=4
   -D PIN_BOARD_SCL=15
@@ -13,6 +14,7 @@ build_flags =
   -D LORA_TX_POWER=20
   -D P_LORA_TX_LED=25
 build_src_filter = ${esp32_base.build_src_filter}
+  +<../variants/heltec_v2>
 lib_deps =
   ${esp32_base.lib_deps}
   adafruit/Adafruit SSD1306 @ ^2.5.13