Fix CHANGES.txt to reflect the twisted evolution and current state of the Admin UI "Files" conf directory File Browser.  Moved issue descriptions to the 5.0 section for the trunk-only - but currently disabled (see SOLR-5539) - ability to create and modify files in the conf dir.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1570764 13f79535-47bb-0310-9956-ffa450edef68