Replace the "Identity" value of the "Distance algorithm" parameter with "Similarity"

See, for example, this description of the identity and similarity terms.

As gaps can be taken into account when calculating the distance, it is better to call the value of the parameter "Similarity" instead of "Identity".

Note that the changes will affect the "Distance algorithm" parameter:

• On the "Statistics" tab of the Options Panel
• In the "Generate Distance Matrix" dialog

Please also add a Russian translation of the term ("Сходство последовательностей" or "Сходство").