Small correction to XSD in oet-parser

[ppazos]

I'm trying to validate the OPTs generated by the Template Designer.

The TD is generating a template_id in the definition element of OPTs and this schema doesn't include that node: https://github.com/openEHR/java-libs/blob/master/oet-parser/src/main/xsd/Template.xsd

Current:

<xs:complexType name="C_ARCHETYPE_ROOT">
  <xs:complexContent>
    <xs:extension base="C_COMPLEX_OBJECT">
      <xs:sequence>
        <xs:element name="archetype_id" type="ARCHETYPE_ID"/>
        <xs:element name="default_values" type="DEFAULT_VALUE" minOccurs="0" maxOccurs="unbounded"/>

Proposed change:

<xs:complexType name="C_ARCHETYPE_ROOT">
  <xs:complexContent>
    <xs:extension base="C_COMPLEX_OBJECT">
      <xs:sequence>
        <xs:element name="archetype_id" type="ARCHETYPE_ID"/>
        <xs:element name="template_id" type="TEMPLATE_ID" minOccurs="0"/>
        <xs:element name="default_values" type="DEFAULT_VALUE" minOccurs="0" maxOccurs="unbounded"/>

Example instance generated by TD: https://github.com/ppazos/cabolabs-ehrserver/blob/master/opts/Encuentro.opt

Problematic portion:

<definition>
...
<archetype_id>
  <value>openEHR-EHR-COMPOSITION.encounter.v1</value>
</archetype_id>
<template_id><!-- TD generated this -->
  <value>Encuentro</value>
</template_id>
<term_definitions code="at0000">
...