MULE-7728: Several improvements:
- Improved message management on DefaultMessageCollection constructor.
- Improved EventCorrelator access to flow's exception strategy in order to avoid create the collected message when accessing it.
- Changed default implementation for in memory object store to avoid use a unique map generating low performance when a lot of objects are stored.
Merge pull request #823 from mulesoft/MULE-7728

MULE-7728: Several improvements: