Support spaces in Wi-Fi network SSIDs and passwords

[Dewb]

I'm one of those unlucky people whose home wifi network has a space both in the network SSID and the password. This PR contains the following changes, which allow me to connect:

• Adds a space character to textentry.lua. The space is rendered as a space; a good future enhancement might be to display some kind of dim _ character to make selecting and entering it clearer.
• Quotes the network SSID and password arguments when calling wifi.sh select.

[Dewb]

Area of potential concern: I haven't put any thought yet into the implications of allowing spaces in all other uses of textentry.

[tehn]

thank you!