FreeMarkerEngine configurability

## Feature Request
As BDK FreeMarker template user, i'd like to be able to configure a multiple template loader, the loader path is configurable(filepath or classpath), so that the templates files are going to be loaded from these paths, and will be override according to the loader's order. I'd like also be able to configure the freemarker configurations such like cache and template update delay.

### Description of Problem:
FreeMarkerEngine from BDK2.0 has a private createConfiguration() method, so that cannot be override to have a custom configuration, in addition, each call newTemplateFromFile, or newTemplateFromClasspath will create a new configuration on the fly, this won't profit the template caching from Freemarker, hence we will have a bit performance impact.

### Potential Solutions:
.To see if this is something we'd like to do in BDK, otherwise we already have an custom implementation of FreeMarkerEngine to satisfy our requirement.

... if you've considered alternatives, clearly and concisely describe those too.