refs https://github.com/TryGhost/Team/issues/1290
- changed query param from `filter` to `excludedEvents`
- exposing filter directly creates problems converting back to NQL after parsing+modifying the query
- removes suggestion that raw NQL can be manipulated by editing the URL
- allows us to use a set of well-defined query params to build the underlying filter string from scratch each time a query param changes
- added `<MemberActivity::EventTypeFilter>` that renders a filter button with a dropdown containing a checkbox for each event type
- if no `member` property is set on the members-activity controller (soon to be another query param) any email event types are hidden because the API can't currently paginate those correctly and in any case they would drown out any other type of event
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