story #7511: Call move REST routes instead of remove+add

Change-Id: I17a287247ddceb4bba0d24ee4885967f9fa6c21a
story #7511: better display of placeholder in empty list

Change-Id: I2d77f0a947cc516a330f120071a8a54100e7d6b6
Use transaction for milestone/backlog/backlog_items content modifications

This removes most of 40X and 500 error we got while testing with new routes.

Plus, perf gain, the PATCH drop from 5/16s to 900ms!

Change-Id: Id686f510ff9278693d9f5a86406f8bd88c57f686
Merge commit 'refs/changes/54/3354/3' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Use transaction for milestone/backlog/backlog_items content modifications
  story #7511: better display of placeholder in empty list
  story #7511: Call move REST routes instead of remove+add

Change-Id: I8451ae2642aa43cca1f725ce85750d13c9d06061
This is Tuleap 7.7.99.79

Change-Id: I893b311df3c0c465e53f20dab450fc044b7efa01