[Keymap] German Corne Layout (#17268)

* added german corne

* added symbol layer

* Delete settings.json

revert setting

* Delete keymap.c

* Update config.h

* Update keycodes.h

* Update config.h

* Update keyboards/crkbd/keymaps/JulianTurner/oled.c

* Update keycodes.h

* Update oled.c

added header

* Update keymap.c

added header

* Update keytabs.h

added header

* Update readme.md

* Update rules.mk

* default settings

* Update settings.json

* renamed folder

* revert

* remove c file import and added to rules

* Update keymap.c

* Update keymap.c

* Update readme.md

* Update rules.mk

* updated files from pull request

* fixed issues with merge

* Update keyboards/crkbd/keymaps/julian_turner/oled.c

* Update keyboards/crkbd/keymaps/julian_turner/rules.mk

* Update keyboards/crkbd/keymaps/julian_turner/keymap.c

* Delete keycodes.h

* Update keyboards/crkbd/keymaps/julian_turner/readme.md

keyboards/crkbd/keymaps/julian_turner/layers.h

@@ -0,0 +1,19 @@
+/* Copyright 2022 Julian Turner
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+enum layers { _QWERTZ, _SYMBOL, _NUMBER };