Allow connecting to wifi networks with no password

[martinmurphy]

Allow the option of connecting to wifi networks with no password.
Some hotel and cafe wifi networks do not have passwords.
While it's not ideal from a security point of view, it would be useful to have the option of connecting.
The current version of the software, uses an empty password in the wifi config form to mean use the current password.
I suggest adding an option to allow an empty password to be set