core (common): improved flexibility of jid selector: - JidSelector can now display a custom set of jids, using the new `to_show` property, see comments for details. - a new "implicit_update" property can be set to False (it's True by default) to avoid the automatic "update" on instance initiation. If unset, use must call "update" explicitly.

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4233be74572a1af8eebd502c009a10641c63ca0c 0.7.0a3
5c28cf8815319abd8c963022091cf4726764a3e6 0.7.0b1
51f73d210da908c9fb292e6bd7fda42a9d2b8453 0.7.0