Make checkmarks in Metadata bulk-editing read-only (or remove them entirely)

[Arnei]

When bulk editing the metadata of multiple events, there are blue checkmarks on the left side of the table. As far as I can tell, these are used to indicate that a metadata field was changed. In that case the checkmarks should be read-only, as clicking on them should not do anything. Alternatively, the blue checkmarks could be removed entirely, as we already have green check marks fulfilling that same function.