Reverse complement button for extended DNA alphabet

1. Open a DNA sequence.
2. Open "In Silico PCR".
3. Type a primer sequence: S.
4. Click the "Reverse-complement" button .
   => The sequence becomes "N".
5. Click it again.
   => The sequence becomes "N".
   So, the reverse-complement button doesn't work for sequences of the Extended DNA alphabet.

A sequence of the Extended DNA alphabet is correctly processed in the Sequence Details View, e.g. character, complement to S is S.

Use the same mechanism for both reverse-complement buttons on the "In Silico PCR" tab.