Handle pings occuring when the prompt window is open more gracefully

[mykter]

At the moment the schedulePing function simply skips the ping. See what classic TagTime does - some combo of opening another window if we think the user is "there", and saving a default afk ping?

[mykter]

Current thought: have a pref so you can choose either:

• prompt windows just pile up if you don't answer them
• you get afk tags for any prompts that would occur when another window is open. A notification pops up from the taskbar to let you know what's going on, in case you are in the middle of answering the first.

[mykter]

Have the first prompt window grow a sidebar, which lists all the missed pings. As you save pings they disappear from the queue.