[database] Clean up mri_scan_type

[maximemulder]

Summary of changes

• Add missing foreign keys.
• Rename Scan_type foreign key fields to MriScanTypeID.
• Remove the default value of 0 for mri_protocol.MriScanTypeID (as this is a non-nullable foreign key, I don't think this should ever happen).
• Adapt the existing queries and scripts in LORIS.

Testing instructions

1. Apply the patch
2. Reinstall Raisinbread
3. Test the associated LORIS feature

As we unfortunately have a very loose typing in LORIS, I may have missed a few bugs when adapting the scripts, but we're early on the next version development cycle so I guess it's the right time to do such changes.

Alternatives

• The foreign key fields could just be named ScanTypeID (it's obvious it's an "MRI" scan type).
• Should the files.AcquisitionTypeID also be renamed to files.MriScanTypeID ?
• Should mri_scan_type.Scan_type be renamed to mri_scan_type.Name ?

Related issues

• Resolves #9284
• Complementary LORIS-MRI PR 1139