Changed default event handler annotation for aggregates to @EventSourcingHandler

For backwards compatibility, the @EventHandler annotation is still supported.
This support will be removed in Axon 3.

Issue #AXON-175 Fixed
Issue #AXON-175 Documented
Changed Cache API to javax.cache.Cache

The jsr107 API has been moved to javax.cache. Currently, Axon supports the 0.5
version of the specification, which has been implemented by the (at this
moment) latest EhCache-JCache implementation (being 1.5.0-0.5).

Future releases of Axon will upgrade the API when an implementation for that
API version is available.

A warning/explanation has been put in the reference guide.

Issue #AXON-81 Fixed
Issue #AXON-81 Documented