Fixing internals of SequenceEnhancer

[bakhtos]

Fixes #17 Fixes #22

[bakhtos]

As was discussed in the meeting:

• Calls to sort_start_timeare removed since this function is removed/no longer necessary. Fixed #17
• After consideration I think that calculation of event lengths should still be the separate seq_len function, since, as Mika pointed out, it is independent of the parser used, so this functionality should not be coupled to event handling in events(). TODO removed and #22 fixed