Refactored MyMesh, advert on doublepress

Pulled the class out of main.cpp, made a header to go along with it, externed globals in headers to make them accessible to button code. Added button code to send an advert on double press. Refactored ini files to prevent linker errors.

variants/xiao_nrf52/platformio.ini

@@ -68,7 +68,7 @@ build_flags =
 ;  -D MESH_DEBUG=1
 build_src_filter = ${Xiao_nrf52.build_src_filter}
   +<helpers/nrf52/SerialBLEInterface.cpp>
-  +<../examples/companion_radio/main.cpp>
+  +<../examples/companion_radio>
 lib_deps =
   ${Xiao_nrf52.lib_deps}
   densaugeo/base64 @ ~1.4.0
@@ -84,7 +84,7 @@ build_flags =
 ;  -D MESH_DEBUG=1
 build_src_filter = ${Xiao_nrf52.build_src_filter}
   +<helpers/nrf52/SerialBLEInterface.cpp>
-  +<../examples/companion_radio/main.cpp>
+  +<../examples/companion_radio>
 lib_deps =
   ${Xiao_nrf52.lib_deps}
   densaugeo/base64 @ ~1.4.0