[enh] display CWConstraint type in its repr
This will change CWConstraint repr from something like:
<Entity CWConstraint 314282 [] at 140127700141904>
To:
<Entity CWConstraint 314282 of type UniqueConstraint [] at 140127700141904>
To help improve debugging UX a little bit.
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)
embedded-javascript-library usr/share/cubicweb/cubes/shared/data/jquery.js