New mode of input selection (UI for Fragment Knitting)

[phraenquex]

Needed fo #1057 .

Selection of protein needs to trigger additional files to be sent to the job (mol, apo).

Needs new mode of selection.

Does not affect what the UI looks like; just changes what the UI does behind the scenes when "submit" is clicked.

Specifically:
If you've clicked 3 alignments (LHS), frontened needs to send to backend pairs of (apo-desolve.pdb, ligand.mol), for each of the selected inputs.
Will be behaviour configured for the job.

[phraenquex]

Doesn't need FE changes after all. Yay