Remove 'has' prefix from JSON-LD terms

[gaurav]

Several terms in the PHYX JSON-LD representation include a 'has' prefix that look somewhat ugly in JSON and in Javascript. We should be able to rename these JSON-LD terms without too many other changes.

These are:

• hasRootNote => rootNodes
• hasSpecifier => specifiers
• hasInternalSpecifier => internalSpecifiers
• hasExternalSpecifier => externalSpecifiers
• [ ] hasComponentClass => componentClasses -- no longer used

Note that phyx2owl.py also uses these terms, so any fixes will need to happen in both places at once.