MULE-7277 Use a LoadingCache rather than providing Callable with get() operation.  This change not only make sense in this scenarios, but testing also shows that this improves performance.
MULE-7277 Deprecate methods not required after refactoring of MVELExpressionLanguageContext for performance.
MULE-7277 Reverty earlier change so that Event context does extend Message context again.
MULE-7277 Create GlobalVariableResolverFactory just once, update ExpressionLanguageExtension javadoc to clarify what context is available.
Merge branch 'mule-3.x' into mel-performance

Conflicts:
	core/src/main/java/org/mule/el/mvel/MVELExpressionExecutor.java
MVEL-7277 Add comment to deprecation in ExpressionLanguageContext
MVEL-7277 Use Javadoc for deprecation comment
Merge pull request #469 from mulesoft/mel-performance

MULE-7277 Various MEL performance improvements and cleanup