Revisit supporting namespaces

[jasmith-hs]

This PR builds off of @pastorcmentarny's PR #306 with a few modifications:

• Allows multiple namespaces in any context
• Allows namespaces to be constructed like in Jinja with an optional dictionary to initialize with and optional keyword arguments
• Makes Namespace an extension of HashMap<String, Object>
• Also adds necessary logic for namespaces to work with eager execution.

This PR will close out #274