wx Alarms: Improve code
wx Alarms: limit the number of alarms shown at once

Addresses #313
wx Alarms: Store attribute
wx Alarms: Rename method and always update the widgets
wx Alarms: Simplify code
wx Alarms: Store hidden alarms

Addresses #313
wx Alarms: Introduce panel for managing hidden alarms

Addresses #313
wx Alarms: Manage hidden alarms

Fixes #313