[UI] Add volume labels to user volume slider
[UI] Don't share XAML icon resources
Refactor volume/gain, improve equation

This reduces the number of conversion places to one, everything deals in
gain except the view model.
Make GbClient connect finish on formal connected

Fixes #51
Kill VolumeForm
Better correct gain/volume formulas
Correct gain/volume formula
Add TextButton
[UI] Volume labels clickable to set