Raise exceptions for unexpected KLIFS pockets

Description

Handle unexpected KLIFS pockets. Detailed description: #86

[x] Case 1: What if missing residues in sequence are not missing in structure (file)? Should not happen; inform KLIFS maintainers.
[x] Case 2: What if KLIFS pocket sequence not 85 residues? Some kinase structures are quite irregular but will stay in KLIFS for completeness; just raise an error in opencadd indicating a problematic structure.

[x] First round: Raise specific exceptions:
- [x] Case 1: Missing residues in sequence are not missing in structure (file)?
- [x] Case 2: KLIFS pocket sequence not 85 residues?
[x] Second round: Can any of these exceptions be fixed - in KLIFS or in opencadd?
- [x] Case 1: Yes, this should not happen in KLIFS, thus the fix lays with KLIFS. But: Keep exception in opencadd to catch more of such irregularities.
- [x] Case 2: No easy fix right now in KLIFS. Keep exception in opencadd so that structure can be skipped in downstream applications such as kissim.