Fix GATT client startup process

For safety reason, we will register GATT client only after adapter is
enabled. That way we ensure that GATT profile is really initialized.
We can unregister GATT client if adapter will be disabled.
Document the limitations when registering a GATT client
Add helper to transform address byte array in string

This helper can be used to transform bluetooth address in human readable
string format.
Parse adapter properties
Change bluetooth address string prints to use ba2str

Replace any conversion of bluetooth address to use ba2str improving the
readability.