tasks #7479 Refactor REST user management

Split REST user management and access to API verification

Change-Id: I03ef4ec506ea30807408b9c4d7d759c2d15c3979
tasks #7486: search user with exact match

Change-Id: If32d29034b45c3fda5a27be1e8ea22a1ff77cacc
Merge commit 'refs/changes/52/3052/2' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  tasks #7486: search user with exact match
  tasks #7479 Refactor REST user management
This is Tuleap 7.5.99.16

Change-Id: I53a7c1f9d8a598c11110d554127b52e1f48f8571