GBE 434

LayerInfo class contains Map<String, LayerExtraInfo> extraInfo.
CacheInfo is currently the only implementation of interface LayerExtraInfo.
The LayerInfo object can be send to client side.

CacheInfo class implements interface "ServerSideOnlyInfo", but this is never used. This interface should prevent the class to be send to client side, but does not do this currently.
Furthermore, CacheInfo implements Serializable interface, but not all it's fields are Serializable.
These bugs prevent the use of a CacheInfo object (in a LayerInfo's extraInfo field) for layer specific caching.

Solution:
* Make CacheInfo and it's fields fully Serializable.
* Make CacheInfo's fields transient (the fields still need to have a default Serializable behaviour)
* Add a GWT module file for CacheInfo and it's specific field classes. This module would be necessary in case of using CacheInfo in configuration.