Issue: SPR-11746

 This commit separates the BackOff configuration from an actual
 execution. BackOffExecution now contains all the state of a
 particular execution and BackOff is only meant to start (i.e.
 create) a new execution.

 The method "reset" has been removed as its no longer necessary:
 when an execution does not need to be used for a given operation
 anymore it can be simply discarded.

 Issue: SPR-11746

Prior to this commit, DefaultMessageListenerContainer was recovering
on failure using a fixed time interval, potentially in an infinite way.

This commit adds an extra "backoff" property to the container that
permits to fine tune the recovery interval using a BackOff instance.

FixedBackOff provides a fixed interval between two attempts and a
maximum number of retries. ExponentialBackOff increases an initial
interval until a maximum interval has been reached. A BackOff instance
can return a special "STOP" time value that indicates that no further
attemps should be made. DefaultMessageListenerContainer uses this
value to stop the container.

protected method "sleepInbetweenRecoveryAttempts" has been renamed
to "applyBackOff" and now returns a boolean that indicate if the
back off has been applied and a new attempt should now be made.

Issue: SPR-11746