Ensure transaction thread local gets cleared for every request and service run (potential deadlock fix)

Need to create a web filter that cleans the thread local that is used by transaction code to hold the database connection during a transaction. The web filter needs to log warnings when it finds the thread lcoal uncleared. The same thread lcoal clearing code needs to to be put into the service runner.

Also need to fix up org.ofbiz.core.entity.TransactionUtil, such that the thread lcoal is cleared in the finally block (just in case).

Remember that no JIRA class should interact with org.ofbiz.core.entity.TransactionUtil directly. JIRA's classes should call methods on com.atlassian.core.ofbiz.util.CoreTransactionUtil, which should in turn proxy calls to org.ofbiz.core.entity.TransactionUtil.