Add a minimal WAR POM

The idea is to add a new xwiki-platform-distribution-war-minimaldependencies module with a pom.xml listing the minimal dependency list for xwiki to start and work (with a minimal feature set).

There are 2 goals for doing this:

1. For our functional tests so that they 1/ execute fast on a minimal WAR and 2/ bring what they need as dependencies
2. So that we can work on reducing the minimal list as we refactor XWiki and make all features pluggable.