File Cache Store Redesign

Hello Team,

I have been using Infinispan on projects for about one year ago, I found it really interesting, so I was recently interested in contributing to the project.

I developed a PoC for FileCacheStore, using [1] and [2].
This implementation is based on the following features :
* Data is stored in append-only files 
* There is always only one active file where data is written
* All valid entries from non-active files are persisted to disk, improving fast loading of cache
* There is a Compaction process who reclaims wasted space by rewriting all live entries from old files to active file

It is actually quite similar to bitcast, but compaction approach is different.

The code is available for review and maybe integration. 

[1] https://community.jboss.org/wiki/FileCacheStoreRedesign
[2] https://github.com/infinispan/infinispan/pull/1282

Your thoughts ?

Cheers
Patrick Azogni