Concatenate a list of epochs into one epochs object.
Parameters:
epochs_list:list
list of Epochs instances to concatenate (in order).
add_offset:bool
If True, a fixed offset is added to the event times from different
Epochs sets, such that they are easy to distinguish after the
concatenation.
If False, the event times are unaltered during the concatenation.
Returns:
epochs:instance of Epochs
The result of the concatenation (first Epochs instance passed in).