Add battery sensing (mostly) for TBEAM0.7

However, disabled until someone with suitable hardware can test and report
back.

@slavino and @tschundler would you be willing to try it with your boards?

You'll need to uncomment the following line in configuration.h

// #define BATTERY_PIN 35 // A battery voltage measurement pin, voltage divider connected here to measure battery voltage

platformio.ini

@@ -9,7 +9,7 @@
 ; https://docs.platformio.org/page/projectconf.html
 
 [platformio]
-default_envs = tbeam 
+default_envs = tbeam
 
 [common]
 ; common is not currently used
@@ -69,7 +69,8 @@ lib_deps =
   https://github.com/meshtastic/SparkFun_Ublox_Arduino_Library.git
   https://github.com/meshtastic/RadioLib.git#d6b12f7eb0a06bd2414c79b437b25d377e3f603f
   https://github.com/meshtastic/TinyGPSPlus.git 
-  
+  https://github.com/meshtastic/AXP202X_Library.git#8404abb6d4b486748636bc6ad72d2a47baaf5460
+
 ; Common settings for ESP targes, mixin with extends = esp32_base
 [esp32_base]
 platform = espressif32
@@ -99,7 +100,6 @@ extends = esp32_base
 board = ttgo-t-beam
 lib_deps =
   ${env.lib_deps}
-  https://github.com/meshtastic/AXP202X_Library.git
 build_flags = 
   ${esp32_base.build_flags} -D TBEAM_V10