Move to Java 8 as minimum version

Creating the issue to link with other issue and list pros/cons.

Pros

Java 7 is end of life since April 2015.

It brings Default Methods which would make retro compatibility a lot easier for us (it's very hard to add new features to existing API right now).

Required for:

• Infinispan 8
• JGroups 4
• Jetty 9.3+

Nice to have

• Lambda Expressions
• Repeating Annotations which would probably allow us to use several times @Named instead of @Component(hints={"hint1", "hint2"}) for example
• New date/time APIs (pretty much what is in Joda Time). We should refactor our $datetool velocity tool to make the java.time api available from velocity

System requirement: http://java.com/en/download/help/sysreq.xml