Add a default ES mapping for ecm:title

Under certain circumstances, the field ecm:title is incorrectly auto-mapped to an ES numeric or date type. The consequence is that the ES index is unusable since it rejects all documents with a dc:title property value that is non-numeric or not-a-date (which is most of them).

The incorrect auto-mapping may happen when an ES full reindex is initiated and the first document re-indexed has a "dc:title" property whose value is a valid number or date. When an ES full re-index is, the error is triggered.

One solution is to set a default mapping for ecm:title in templates/common-base/nxserver/config/elasticsearch-doc-mapping.json, for example

    "ecm:title": {
        "type": "keyword",
        "ignore_above": 256,
        "copy_to": "all_field"
    },