[REVIEW] code review / suggestions

This is not for merging but rather a code review of the AASequence interface. There are a lot of functions that were maybe well-intended but are not used a lot and just seem like clutter to me at the moment. 

I suggest to remove functions that are redundant or perform implicit type conversions that are quite expensive (e.g. String to AASequence). This should rather be done on the user side and make him/her aware of the costs.