[backport 5.0] Configure visit store via JNDI

For end-projects using relevance make the following changes:
1. Add an Environment entry to context.xml:

    <Environment name="elasticsearch/targetingDS" type="java.lang.String"
                 value="{'indexName':'visits', 'locations':['http://localhost:9200/']}" />

2. If still present, remove all datastore bootstrap configration, because all defaults are provided by targeting.
3. If present, remove datastore related entries from DummyEnvironmentSettings because datastore config management is now done via JNDI instead of envsettings.