fix missing text and label `connecting`

closes #192 (closed)

In addition to the title, this MR improves the start/stop button animations. We only set a static button background on animation end in case the current vpn state is still the same the animation was animating to. If different VPN states such as Disconnected -> Connecting, Connecting -> Connected follow after each other quicker than the UI animation takes, just continue animating to the current state instead of setting a static button background in between.