Choose & update logging framework for 3.x

We need to decide upon the logging framework which we'll use in 3 and update the code (including extensions) accordingly.

Current state of affairs is:

• the core modules (jcr, schematic etc) use the logging from modeshape.common.util, which uses SLF4J api behind the scenes
• the sequencers (and possibly other extensions) use SLF4j directly (just the api)
• the tests use SLF4J fully (via the log4j adapter)

We need to take into account that we will deploying into AS7, which may not have support for SLF4J.