Add European Student Identifier to Learner

[geirmv]

A proposal from the EDSSI project:

Add European Student Identifier as a new identifier type for Learner.

The identity is relevant for the use of ELMO in EWP, and also for EMREX.

It has been defined as part of the MyAcademicId project, in the context of SCHAC

[geirmv]

                                                <xs:documentation>Currently there are only two predefined types you can have here:

                                                    nationalIdentifier - if present, then the value of it should contain the
                                                        &quot;primary&quot; national identifier of the student. For more information on
                                                        national identifiers used for various nationalities, see:
                                                        https://en.wikipedia.org/wiki/National_identification_number

                                                    esi - European Student Identifier. For more information see:
                                                         https://wiki.geant.org/display/SM/European+Student+Identifier

                                                    You can also have any number of custom types. Contact us if you'd like
                                                    them added to the official specs.
                                                </xs:documentation>

[geirmv]

The issus has been solved as part of ELMO 1.6