Do not hard code columns definition

This is a first step to bring dynamics into kanban columns. It
introduces a new GET /kanban/:id that furnish columns definition.

Please note that the color definition is missing.

Part of story #7577 display a Kanban cardwall.

Change-Id: I98bd05d1542135f0da11eb58eb00c02f2fda61d2
Merge commit 'refs/changes/21/3321/9' of ssh://gerrit.tuleap.net:29418/tuleap into tuleap-stable-master

* ssh://gerrit.tuleap.net:29418/tuleap:
  Do not hard code columns definition

Change-Id: I3719073b405836be1e1f3a338450e948a32ac104
This is Tuleap 7.8.99.5

Change-Id: If233b5e68cb5995c5f53039f8aa2a19d81507781