Support server acl events

CMakeLists.txt

include/mtx/events/collections.hpp

include/mtx/events/event_type.hpp

include/mtx/events/server_acl.hpp

include/mtxclient/http/client.hpp

lib/structs/events.cpp

lib/structs/events/collections.cpp

lib/structs/events/server_acl.cpp

lib/structs/responses/common.cpp

tests/events.cpp