conflict editor should give clearer warnings and colour-coding

[Polarbear]

The conflict editor pops up when joining ways with conflicting tags or relation memberships.

When the ways have lots of tags, the conflicting ones are only obvious when the 'conflicts only' box is ticked.

Please make the conflicts more visible, e.g. by colour-coding green and red (as seen in the version conflict resolver).

Please do not make any resolutions standard, since they can be wrong but not obvious enough (e.g. I have river sections that are boundary=administrative, while the next section is not).
Also the semicolon-proposal for resolving name conflicts is not nice and often wrong.

The dialogue should only allow to be applied when conflicts have been actively solved.

For the relation memberships, it should be listed in which relations the join-candidates are members.