Multiple enhancements to support more flexibility in configuration

[jguertin-gls]

This change set address a few issues, which were implemented by us specifically to support the ability to have indexes that support multi-tenant databases. Specifically, we did the following:

• When using "only" in the mapping, transient properties will now be allowed
• "indexId" may now be added to mapping which will allow a change to which field is used as _id in the index.
• Additionally, "indexId" will support multiple fields
• Corrected a problem where counting the instances of a domain class sometimes occurred using the wrong hibernate session

[jguertin-gls]

By default, indentityProperties will behave as it did before, using the identifier as the sole property for indexId.

[jguertin-gls]

This change will allow for an 'indexId' property to be added to the searchable closure. This value can either except a string, a list of properties or a map. The properties listed in 'indexId' will be concatenated together to form the _id value in the index, with a separator between them. The default separator will be ':', but this too may be overriden. Here are some examples of what it may look like, within searchable {}:

indexId = 'uniqueValue' // _id would contain the value of the 'uniqueValue' property
indexId = ['id', 'distinguisher'] // _id will be '<id>:<distinguisher>'
indexId properties: ['id', 'distinguisher'], separator: '-' // _id will be '<id>-<distinguisher>'