Support for addons

[abhin-rk]

I recognize that this is a big request. But it would be awesome if there were external packages that could integrate with this app easily through a plugin system.

For example, I'd like to set my slack status at work to indicate that I'm in a pomodoro and if possible even indicate how much time I'll be in a pomodoro. I'm sure many people have many such integrations they'd like to see. But it's infeasible to expect the core team of pomotroid to implement all such integrations. But if the community were allowed to create small packages that could receive events for various things in pomotroid, that would make the app instantly better than every other pomodoro app out there.

The whole system could even be as simple as using webhooks. The user could configure URLs that would receive a request when various events happen. Or it could be as complicated a plugin system that has autodiscovery of plugins and one-click installation. I guess that's up to the core team to decide based on the resources available.

[dvogtfstr]

I would also like to have any possibilty to trigger something on state change. Maybe just a run command option for statechanges would be enough for the first time 👍🏾