Some more Polari string changes

Hey folks,

we've just done a couple more string changes in Polari:

- we've decided that "Network" is a much better fit

than "Connections" (which we've really only used

because the initial mockups did), so:

"Connection Name" => "Network Name"

"Add Connection" => "Add Network"

"Custom Connection" => "Custom Network"

"Connection foo has an error" => "Network foo has an error"

(I am sorry about the back and forth on the first label - I know this

is the third change in a month or so :-( )

- we've removed a rarely used dialog, and when doing that it

seemed appropriate to update the accessible name of a button:

"Join room" => "Add rooms and networks"

Cheers,

Florian