cubicweb #17254012 Allow to set version from vcs and stop expect it from __pkginfo__ [open]

Using allow to manage version from mercurial tags and allow to work with intermediate versions.

cubicweb currently read cubes versions from, to make this work it should read them from pkg_resources API instead.

Also we must check that migration system doesn't break with intermediate versions like "X.Y.Z.devP+hgHASH"

done in<not specified>
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