Fix bugs #2705 (https://tuleap.net/plugins/tracker/?aid=2705)

== /!\ Backward compatibility restore /!\ ==
* Restore updateArtifact and addArtifact behaviour at 2.0.3 for 'value' field of FieldValue type.
  It allows again to use strings and no longer understand ids.

  The new recommended way to manage list values (Selectbox, MultiSelectBox, CheckBox and OpenList) is
  to use the new field 'bind_value' of FieldValue type.

* WSDL update: FieldValue 'field_value' as a new choice 'ArrayOfTrackerFieldBindValue'.

* Performances: Activate WSDL cache. ~20% performance boost on average operations.
Merge commit 'refs/changes/21/321/1' of http://gerrit.tuleap.net/tuleap into tuleap-stable-master

* http://gerrit.tuleap.net/tuleap:
  Fix bugs #2705 (https://tuleap.net/plugins/tracker/?aid=2705)
Tuleap 5.11.99.10