SLING-3411 - Enable configuring the maxCallerDataDepth in Logback LoggerContext

-- Added config for specifying the maxCallerDepth
-- Updated doc around Logging pattern. It now refers to Logback config docs

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1571318 13f79535-47bb-0310-9956-ffa450edef68