RF: Make Dataset.id independent of annex.UUID and also for non-annex datasets

[mih]

all with UUIDs

[mih]

Ideally, this would be merged on its own, but it is only really needed for #682 at this point, hence I'll merge it in there if necessary.

[coveralls]

Coverage increased (+0.004%) to 86.776% when pulling 3b8431e on mih:rf-rethinkid into 9a6ad90 on datalad:master.

[coveralls]

Coverage increased (+0.004%) to 86.776% when pulling 3b8431e on mih:rf-rethinkid into 9a6ad90 on datalad:master.

[coveralls]

Coverage increased (+0.004%) to 86.776% when pulling 3b8431e on mih:rf-rethinkid into 9a6ad90 on datalad:master.

[coveralls]

Coverage increased (+0.004%) to 86.776% when pulling 3b8431e on mih:rf-rethinkid into 9a6ad90 on datalad:master.

[coveralls]

Coverage increased (+0.004%) to 86.776% when pulling 3b8431e on mih:rf-rethinkid into 9a6ad90 on datalad:master.

[codecov-io]

Current coverage is 86.77% (diff: 100%)

Merging #747 into master will increase coverage by <.01%

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  Misses         2366       2366          
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[yarikoptic]

@mih crazy day -- everything conflicts... otherwise I have no objections since I lost a good grasp of the ids until I will try more and see.