Add non-canonical basepairs per PDB file

[AntonPetrov]

The non-canonical basepairs should be included as separate lines for each PDB. These lines should appear in separate SEED files because there will be lots of lines that may not be relevant for all users.

As a further enhancement, the Rfam website could serve SEED alignments using an API with optional flags for showing motif annotations, non-canonical basepairs, and other information.