Dev/dsl mapping

Now supports the DSL based mapping (docs to follow). The default mapping is now hard coded based on the DSL backing API (default-schema-mapping.conf is deleted).

DSL mapper does startup time checking of:
- field existence on the Avro record
- type match of the value being mapped and the target Avro field
- type match of a literal being mapped and the target Avro field
- the ip2geo DB being configured when using ip2geo fields (this is different from the config based mapping, which treats ip2geo fields as not present when the DB is not configured)