Move to a lighter cache system

Infinispan does many things but we need very few of those and there is other lighter cache systems out there.

Infinispan weight 4.6M in the XWiki WAR.

Here are some ideas:

• http://www.ehcache.org/ (1.7MB for the 3.4.0 version but we actually already embeds it through Tika)
• https://commons.apache.org/proper/commons-jcs/ (522kB for the 2.2 version)
• https://github.com/ben-manes/caffeine (984kB for the 2.5.6 version but we actually already embeds it trough Solr)