_prepare_continuous_data doesn't return correct path

[cxrodgers]

As written, the v0.5 of _prepare_continuous_data return a path called something like
/data/TASK_NAME/S00_STEPNAME/session_N
instead of
/data/TASK_NAME/S00_STEPNAME/continuous_data/session_N

The problem is here:

autopilot/autopilot/data/subject.py

Line 787 in 04b5968

continuous_group_path = '/'.join([group_path, group_name])

The node is correctly created but the wrong path is returned (and then sent to _data_thread, causing problems).

For an example of a fix, see here: https://github.com/Rodgers-PAC-Lab/autopilot/blob/20decc5168ba2613f973a4c044101542dee47879/autopilot/data/subject.py#L820