hold events not synced

[leoscholl]

for the last target in a sequence, there should be a "cursor enters target" event which is currently not being sent.

also, currently the trial structure is a bit confusing in the sync'd events since there is only a "trial end" event when a wait state begins, but not when a target gets repeated due to an error (assuming the number of tries is greater than 1)

[leoscholl]

probably while fixing this bug we should also separate the delay period from the hold, so we have (on a central target)

target -> hold -> delay -> go cue

or (on a peripheral target)

target -> hold -> reward

[leoscholl]

5f4d7e59ec14ccfd5fba1bd5d5f3eab0b4ee06f9