Support for connecting to multiple vpns

[dh-linetco]

Currently it is impossible to activate a second vpn while being connected to another one using only the budgie-network-applet. Also radio buttons should be probably checkboxes then, as radio buttons normally signal that you can only choose one option. Also see https://github.com/elementary/wingpanel-indicator-network/issues/160

[fossfreedom]

Seems like a great idea. I have marked this with a help wanted label.

[sempasha]

@fossfreedom I'll try to get into this issue and will try to fix it.