Share option for external plugins

[LuisHPorras]

Hi!

First, thanks a lot for the plugin development! 😄

Use case

We are using the EventOrganizer plugin to publish events on multiple WordPress sites and to publish fromthose sites to an external event calendar service, Gancio. Gancio its a federated event calendar (free software) that receives events from different sources (including WordPress instances). Currently, Gancio has a simple WordPress plugin that hooks in the EventOrganizer life-cycle and publishes the events created. We'd like to be able to choose whether to share an event to a third-party service or not.

Giving it a thought we think this could be a feature that other plugins may use and that maybe makes sense to develope inside EventOrganizer.

Feature description

Add a "share" option (checkbox) in the event details section to allow third-party plugins to handle the sharing of the event.

Note

I've being playing with the code and I've built a first iteration of this feature although I'm not familiarized with the code so it's probably not the best thing. I'll create a branch and make a MR in case you are still active with the development.