added links to index and constraints to rest api root
added index listing
added list of rest api surface endpoints
Unique constraint verification: Use document frequency

This is provided directly by lucene so we don't need to maintain an
external term counter.
Depend on the correct Java version

The Oracle JVM has a different package name, which will be addressed
in a future commit.
Merge pull request #1804 from apcj/term-freq

Unique constraint verification: Use document frequency
Merge pull request #1749 from lassewesth/restapiindexlink

added links to index and constraints to rest api root