Refactoring for SIS-184 : (properties refactoring were missing) MappedByteBuffer is ejected from Database class and put into internal classes in order to be upgraded to something better later.

git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK8@1647217 13f79535-47bb-0310-9956-ffa450edef68