* Move isdevice validator under helpers.config_validation.
* Check that all persistence files are set and are unique if any is set
by user. This is necessary to avoid file name clashes.
* Check that a set persistence file has an existing and writable
directory.
* Check that a device is either a valid device file, "mqtt", or a valid
domain name or ip address.
Martin Hjelmare
Pascal Vizeli
Fabian Affolter
Malte Deiseroth
Paulus Schoutsen
deisi