Add Contra shield (#633)

* Add Contra Shield (#1)

* Add bluetooth control layer to contra keymap (#2)

* fix contra keymap issues

* add bluetooth control layer

* clean up contra files

* add contra.conf file

* add missing bracket for default_layer

* update copyright year to 2021

* add contra metadata file

* refactor pro micro overlay for new syntax

app/boards/shields/contra/contra.zmk.yml

@@ -0,0 +1,8 @@
+file_format: "1"
+id: contra
+name: Contra
+type: shield
+url: https://github.com/ai03-2725/Contra
+requires: [pro_micro]
+features:
+  - keys