Enable support for event-based parallel task execution

[agonper]

The main aim of this PR is to allow to execute tasks in parallel in reaction to any event that becomes triggered. To achieve that the following elements have been implemented:

• A TaskGraphBrowser class, which records the tasks and the events that conform the currently loaded application task graph. A singleton of this class has been implemented. It can depict the whole task graph, the relationship between tasks (by means of invocation and output events) and detect cycles. Useful to debug any loaded application task graph.
• A TaskGraphPlannerParallelizer class, which intervenes each call to the main application task planner, consults the graph browser to spawn new child events from a parent event which triggers multiple immediate tasks and / or task schedulings. It propagates timeout notification to children task chains and funnels child task chain finalisation events. The main application task planner has been updated to use an instance of this class.

Aside from this main aim, other things have been solved:

• Updated README.md to remove one of the main limitations of the plugin 🎉
• Demo application task graph has been updated to harness parallel execution possibilities 😎
• Demo application now prints application task graph upon load 🤓
• A bug in the internal event manager has been caught and controlled for now, must be watched 👀
• Testing API has been improved to reduce setup code when testing custom tasks in depending apps / plugins
• Improve task error logs with a complete stack trace
• Logging traceability has been improved to identify where child events are being spawned, both in event-based and scheduling-based triggered tasks
• Now if at some moment the app is going to require to schedule tasks below 15 minutes windows, the user will be asked to disable battery optimisations from the very beginning. Previously, it was by the time the concrete task with that requirement was going to be planned ⏲️
• Having a task that requires to run in the foreground in the middle of a task chain is no longer a limitation. The task graph browser is used to detect dependencies between tasks and a whole new foreground checker has been implemented to check for foreground execution up in the task chain ⏭️
• Demo's home screen has been updated to point to looking at the logs to see how the plugin works 📱

[matey97]

Well, I think I understood almost everything 😵 and I have only one thing to say: Wow, very clever work Alberto! 👏

[agonper]

Thanks Miguel! It's a bit crazy, indeed. But it works and I think it is resilient. I'm going to merge #9, then I'll propagate the changes to this branch to see that everything is working as expected. Once done, I'll let you know to give it a last look. Many thanks for your time 😉

[agonper]

Done @matey97! Seems to perform well. Could you have a look to the latest changes? Also, it could be good if you could run the tests and the demo app on your devices to see that everything is working as expected. Whenever you have time, don't worry. Many thanks in advance

[matey97]

I ran the tests and the demo app in my devices and all work as expected!! Nice work!!