New UX for upload conflict resolution

### Is your feature request related to a problem? Please describe.
Resolving upload conflicts is a time consuming task involving several well-aimed tips for each conflict to resolve.

### Describe the solution you'd like
Redesign the list shown in the conflicts section of the uploads dialogue. Rather than the one preview image shown now, show the local version (file that was requested to be uploaded) on the left (as now), and the preview of the current remote file on the right. Make these list entries swipable. Swiping from left to right (local to remote) triggers the "keep both files" function, uploading the local file under an distinctively extended filename next to the existing. Swiping from right to left (remote to local) triggers the current "keep original" function, however with bug #8923 fixed. The current "keep local" function, overwriting the existing remote file would be available from the context or overflow menu only.

### Describe alternatives you've considered
n/a

### Additional context
This behaviour would make a lot of sense if feature request #8948 was implemented, as no conflicts would show up where both files are already technically identical.