Connection event type checkboxes are horrid and confusing

Currently, we have checkboxes like so in our widget:


The problem with these checkboxes, is that they are confusing and don't conform to what people would expect them to do.

- For instance, checking the top level "issues" checkbox will enable all issue events by adding the "issue" type to your allowed list.
- However, **disabling** it but leaving all the child items ticked will do the same thing.

I think generally it would be better to do away with the root checkbox items entirely, and instead move to a model where we just explicitly opt into each and every feature, rather than having parent and child event types.

Start by locating the widget implementation for the connection event type checkboxes and the code that builds the allowed event-type list. Confirm how parent and child selections currently map to that list, then update the UI so each feature is opted into explicitly and verify that the resulting selections match the displayed checkboxes.

Written by the indexing model from the issue text.