Add Import Templates + Add Checkbox for Non-Default Baan Codes + Include Training in Coordinator Exports

Description

• Add templates for job offer and extra work imports
• Add a checkbox for non-default baan-codes on job-offer creation - this requires merging of frontend!1 (merged)
• Adds a column for each possible training for every student in coordinator exports of applications

Related Issues

• Resolves #171 (closed)
• Resolves #114 (closed)
• Resolves #160 (closed)

Checklist

• I have added a changelog entry to reflect the significant changes I made.