We're filtering the events using `Event#visible_to_user?`.
At most we're loading 100 events at once.
Pagination is also dealt with in the finder, but the resulting array
is wrapped in a `Kaminari.paginate_array` so the API's pagination
helpers keep working. We're passing the total count into that
paginatable array, which would include confidential events. But we're
not disclosing anything.
This optimises how GroupProjectsFinder builds it collection, producing
simpler and faster queries in the process. It also cleans up the code a
bit to make it easier to understand.
* Meld the following disparate endpoints:
* `/projects/:id/events`
* `/events`
* `/users/:id/events`
+ Add result filtering to the above endpoints:
* action
* target_type
* before and after dates
