API v1/v2 image update harmonisation

[benjamingeer]

I think it makes sense to do these together:

• Improve bulk import and separate from API v1 #1110 Implement bulk import in API v2
• Don't require Knora and Sipi to share a directory for image upload #535 The integration between 'webapi' and 'sipi' shouldn't require a shared directory

I'd like to do it this way:

1. Implement bulk import in v2
2. Remove API v1 bulk import
3. Refactor API v1 resource and value update code to call v2 update code

This will mean that image creation via API v1 will work like image creation via API v2.

[benjamingeer]

Since we have been rethinking bulk import, this is no longer relevant.