[Misc] Split xwiki-platform-web into 2 modules: xwiki-platform-web-templates...

[Misc] Split xwiki-platform-web into 2 modules: xwiki-platform-web-templates and xwiki-platform-web-war. Rationale: be able to write integration tests for templates more easily (by depending on the new template module rather than having to unpack the WAR, and use a modified velocity engine to read templates from local files)