SPIKE: Investigate feasibility of Groovy Closure based string customisation

Some work required to see whether it's feasible to save and use user-defined groovy closures to customise strings.

We need to know whether allowing users to input groovy closures is going to cause security/performance issues.
Investigate:

• working within a thread with some kind of max-depth to stop loops
• saving closures as strings, then fetching and executing them (database interation, nesting, etc)
• restricting what the closure has access to
• any other concerns which pop up while developing

Git repo exists at: https://gitlab.com/knowledge-integration/spikes/ermproxyspike