JIRA ticket: LIMS-1804

Summary:

Barcode should be a required field for plates

Changes:

• Add a validation of required to the barcode field
• Combine the error message with the message about uniqueness
• If a user does try and add a barcode that is already used, catch the database error and return a sensible message

To test:

• Go to any shipment in any proposal, eg /shipments/sid/65577, and click Add Container
• Create a puck, checking that barcode is not a required field
• Create a plate (eg container type of CrystalQuickX), try to leave the barcode field blank, check you get an error
• Try a barcode that already exists (eg "a"), check you get a sensible error message
• Try a unique barcode, check you can create the plate (no samples are needed)