Integrate usermods environment

Move the "all usermods" logic in to the platformio script, so the
'usermods' environment can be built in any checkout without extra setup
commands.

platformio.ini

@@ -632,3 +632,4 @@ build_unflags = ${common.build_unflags}
 build_flags = ${common.build_flags} ${esp32.build_flags} -D WLED_RELEASE_NAME=\"USERMODS\"
   ${esp32.AR_build_flags}
 lib_deps = ${esp32.lib_deps}
+board_build.partitions = ${esp32.big_partitions}