* Fix intermittent links bug - graph.links Map()
Replaces graph.links with Map()
Adds a Proxy to provide for...in and indexer access
Temporarily uses merged Map+Record type, to ease downstream migration
* nit - Remove redundant code
* nit - Remove redundant null checks
* Add Serializable interface, used in LLink
Allows LLink to be serialised as an object rather than an array, bringing it inline with the rest of LiteGraph.