examples: Fix incorrect category heading
examples: shorten coap folder name
static-tests/examples: check subfolders for entries
ci/test_native: Adjust to new examples structure
examples: adjust makefiles to new structure
ci/tests: Fix symlinks to point towards proper examples
Since the native process is a child process of pyterm when called via
make we need to dig deeper for riotctrl. This also means that we require
pyserial to execute it.
