Allow lab to pick which lane a pool goes into on Prepare Sequencing Run page

Currently lab sometimes prepares sample sheets one lane at a time. Continuing to support this workflow would require ability to pick a specific lane for a particular pool rather than having the pools be assigned to the lanes in order of addition (so that first pool added is ALWAYS in lane 1, and there can't be a pool in lane 2 unless 2 pools--or two of the same pool--are added).
Raised in shotgun walkthrough 07/31/2018