WIP: Feature/add countdown timer

Work-in-progress merge request

This adds a "Countdown Timer Plugin" to OpenLP.

Two operational modes are available:

  • Countdown to specific time (i.e. 10:00 AM)
  • Specific-duration countdown (i.e. 5 minutes)

I began this in 2014, but got completely sidetracked and forgot about it until now, so I'm trying to update the code to match the master API.

Merge request reports