Improve auto-annotations behaviour with long sequences

Introduce special restrictions for auto-annotations, which control if they should be turned on automatically when new sequence is opened. Currently this is done based on the previous case of using auto-annotations, which is not always best strategy. For example, for long sequences searching for enzymes or ORFs may take a long time and usually is not required, thus the auto-annotaions should be enabled automatically only for sequences within a reasonable size range ( =< 10KB ).