add new tasks for playing back experiments

[leoscholl]

cursor only task would be useful for playing back motion data reading from an hdf file the target positions and timing would be useful to reconstruct previous experiments

[leoscholl]

tried to implement in 821b26ed64e16e9b96274e4af2bb4394e246b94c, but it's harder than i thought; basically any slight difference in the cursor position has profound consequence on the rest of the task. in theory it should work, so maybe there are some bugs either in the task or elsewhere. but either way this is probably not going to happen