Make a visual difference on tray icon between "idle reseted" and "just started"

[george9816]

I start Pomotroid with a global shortcut and I would find it useful to see if it has realy started.

Practically, the tray icon is the same between reseted and just started states (i.e. a red circle). Some visual difference like a play sign when reseted or anything else would be convenient.

[flowrean]

This is somewhat related to #422.