Migrate Jalview JPred Client to use Slivka's JPred Services

In Jalview 2.11 and before JPred is called via legacy jws1 code.
* JPred Services for slivka need to be specified for single sequence and alignment based prediction modes
* JPred client code from the jws1 client needs to be rescued and adapted for the refactored web service model introduced in Jalview 2.12.
* Decisions need to be made about:
1. Whether alignment based JPred predictions are run like AACon services - ie as alignment calculations
2. Whether the user is allowed to submit several sequences at once to JPred's sequence based prediction service (which generates a multiple sequence alignment for each input sequence).