Unify specification versions in Weld 2.2 documentation and examples

Specification versions should be unified throughout the documentation and examples.
This pertains to mentions of the spec version in text ("...to any other container that supports Java EE 6...", etc.) but also to links to descriptors and XSDs (application, web, faces-config, beans, ..) in code snippets and examples.
There are now some mentions to EE6, some to EE7 (sub-)specifications.

I'm not sure if we should go EE7 all the way, or retain mentions to EE6 in sentences like "...can be run on a wide range of servers, including [...] and any compliant Java EE 6 container...".
The examples are still runnable on EE6 servers.