Use HSSP and DSSP cache for non pdb sequence input types

[jonblack]

When the PDB accession code is known, the cache should be used. This is possible for all jobs apart from sequence-based jobs.

The new accession code method (#18) can be used directly; the pdb content method will require parsing the accession code.

[touwwouter]

@jonblack do you think this can be implemented easily, is it necessary, or is this a todo for the far future?

[jonblack]

Using an existing cache from cmbi4 (or wherever it is) isn't difficult. If we want to update that cache with new files, it's a bit more work.