Drop the community only "Integrations Guide" and separate content with these purposes:

• https://github.com/infinispan/infinispan.github.io/pull/237 (improve documentation categories on the site)
• Set up Spring Cache and Spring Session docs for future improvements, such as combined session externalization guide, and downstream deliverables.
• Make the Hibernate content easier to find.
• Move WildFly modules content into Developer Guide.