Cut the following classes over to ImmutableOpenMap:
* MetaData
* IndexMetaData
* ClusterState
* IndexTemplateMetaData
Small cleanup
Added execution option to `range` filter, with the `index` and `fielddata` as values.
Deprecated `numeric_range` filter in favor for the `range` filter with `fielddata` as execution.

Closes #4034
use the proper abstraction of ImmutableOpenMap
we already use the open map / clone trick, might as well use the ImmutableOpenMap here