add support for pooling file generation from multiple library plates

[RodolfoSalido]

Sequencing runs from multiple projects are becoming more commonplace. Combining prep data_frames and calculating normalized pooling volumes from combined project sequencing runs is straightforward, but the current pooling file generation codebase doesn't support overlap on Well_ID from two different prep plates when generating a pooling file. This needs to be fixed.

[AmandaBirmingham]

@RodolfoSalido can you say more about this, or maybe provide a link to the part of the code that needs to be enhanced?