Merge pull request #49 from JamesGlover/add_priority_to_plate

Add priority to plate
Add new classes
Add plate_template model to sequencescape
Update lot and qc models to include relevant info
Add remaining TagQC models to client-API
Remove old puts from code
Conversions can have parents assigned
Merge pull request #50 from JamesGlover/tag_qc_r23

Adds tag QC support to client api
Merge branch 'production' into fail_but_charge