New class for aggregation of fixation and saccade events

Create a new class for aggregation of fixation and saccade events that would allow for gaze interaction events with multiple targets at once.

That means we could have fixationEnd with multiple targets at once... This will be very helpful in dyslexia intervention, where there could be overlap due to buffer zones. Then, there will be an evaluation of whether the desired AOI (word) was in an array of captured targets...

This new GazeAggregation class should accept for registration own elements. In its constructor, it will accept a GazeInteraction object for which it is applicable (not applicable for Dwells, but only Fixations and Saccades atm).