add rollback height to "minimum confirmations" setting

[Maxnflaxl]

Feature title add rollback height to "minimum confirmations" setting

Describe the current situation we have 0..10 blocks

Describe the solution you'd like 0..10,60

Additional context https://github.com/BeamMW/beam-ui/blob/master/ui/view/controls/SettingsGeneral.qml#L102