Changed the build task to no longer set isDefault: true. This lets you
set your own default build task from a code workspace.
Also replaced "cd app" in each command by setting the working directory
for the task.
* Move all headers to `include/zmk` directory.
* Update includes to reference them properly.
* Add `keymap.c` file from keymap, if found.
* Toplevel CONFIG_ZMK_BLE aggregate config setting.
