Add SOAP method getPlateformProjectDescriptionFields

Change-Id: I6395572688ce30c2669f78c1b093129fbc730293
add SOAP setProjectDescriptionFieldValue

* Add or update the value of the given description field for
a given project

Change-Id: Icf61a22b2fbc5cb4aed4451dd1ae2542a36230c1
add SOAP getProjectDescriptionFieldsValue

Change-Id: Ic7e1828bf405a338e061b9da6430e2919060850b
Add verifications in new SOAP description fields methods:

* Project exists on get
* Field exists on set

Change-Id: I22ec344eea1edcac01d428971808ec8bf97a57b4
Merge remote-tracking branch 'gerrit/4209_update_the_description_fields_of_my_project_through_SOAP' into HEAD

* gerrit/4209_update_the_description_fields_of_my_project_through_SOAP:
  Add verifications in new SOAP description fields methods:
  add SOAP getProjectDescriptionFieldsValue
  add SOAP setProjectDescriptionFieldValue
  Add SOAP method getPlateformProjectDescriptionFields

Change-Id: I6a1b7f5a4e790b1550e6585979fae108cc49b464
This is Tuleap 6.3.99.7

Change-Id: I7cf3179c2cb88c22da756672d827b97280a7671b