Feature/batch from web

[jechols]

Closes #220

Refactors batch generation in order to allow for command-line or web admin batch generation. Creates a new section in NCA's web interface for doing batch generation on demand, and a new role for who is allowed to do this.

Normal contributors

I have done all of the following:

• [x] Fixes and new features have unit tests where applicable
• [x] A new changelog has been created in changelogs/ (based on changelogs/template.md)
• [x] Documentation has been updated as necessary (hugo/content/)