The qt, qml, and kivy GUIs have a first-start network-setup screen
that allows the user customising the network settings before creating a wallet.
Previously the daemon used to create the network and start it, before this screen,
before the GUI even starts. If the user changed network settings, those would
be set on the already running network, potentially including restarting the network.
Now it becomes the responsibility of the GUI to start the network, allowing this
first-start customisation to take place before starting the network at all.
The qt and the qml GUIs are adapted to make use of this. Kivy, and the other
prototype GUIs are not adapted and just start the network right away, as before.
(this somehow escaped attention before, as most objects usually don't have multiple instances,
unless multiple wallets are open at the same time.)
Also, move all signal declarations, class constants and variables to the top of class definitions.
