talkatu/talkatu

ebabd7682683
Update TalkatuMessage:id to be a string.

Many modern protocols are using uuids as id's and forcing that into a uint64 is
going to lead to collisions. So instead just use a string which should work for
everything.

Testing Done:
Ran the demo and unit tests.

Reviewed at https://reviews.imfreedom.org/r/879/
Talkatu is versioned in [mercurial](https://www.mercurial-scm.org/) and is
available on [keep.imfreedom.org](https://keep.imfreedom.org/talkatu/talkatu).
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