[BUG] When uploading statements, keep connections

[sverhoeven]

Describe the bug

Given I have a network with driven connections and/or conflicts between statements.
When I upload a statements csv file then all the connections are deleted.

To Reproduce

Steps to reproduce the behavior:

1. Load example
2. On statements table page, download the statements.
3. Upload the statements.csv
4. In network page the driven connections are gone

Expected behavior

I expected the connections that are still valid to remain.
Would be nice if connections will be deleted that I get asked if I want to continue or cancel.