Add sandboxing for GString-based method invocation
Switch to Groovy as the default scripting language

This is a breaking change to move from MVEL -> Groovy
[TEST] Add assertion failure messages
Match query with operator and, cutoff_frequency and stacked tokens

If the match query with cutoff_frequency encounters stacked tokens,
like synonyms in the same position, it returns a boolean query instead
of a common terms query.  However, if the original operator was set
to "and", it was ignoring that and resetting the operator to "or".

In fact, if operator is "and" then there is little benefit in using
a common terms query as a must query is already
executed efficiently.
Be more diligent about ThreadPools having names

Add a name parameter to what was the empty ThreadPool constructor. Assert if the the ThreadPool's setting doesn't contain a name.