Wrong processing of joined annotations by the "Get Sequences by Annotations" worker

The "Get Sequences by Annotations" worker has the "Gap length" parameter that specifies a count of gaps inserted between result sequences corresponding to parts of joined annotations. Currently changing of this value does not affect worker results - sequences for joined annotations are just merged together. It is required to make this parameter work and use the "N" or "X" character as the separator between sequences depending on their alphabet. Finally, it is needed to clarify the description of this attribute appropriately.