Multiprotease search and target/decoy collisions

[Alexander-Sol]

PR #2394 added functionality to eliminate decoy peptides that are identical to target peptides. However, this only works for single-protease searches. If there are multiple proteases, then it is possible to have identical target and decoy peptides again.

Possible solves for this issue:

• Move protein db loading to the SearchTask
• consider all possible proteases in the MetaMorpheusTask
• Decoy on the fly