DDF-733  moved CommonCallback, PropertiesLoader, and STSClientConfiguration to security-core-api in platform app in support of usage by spatial app
DDF-733  updates for refactoring CommonCallbackHandler and PropertiesLoader into platform app's security-core-api
DDF-733  updated to use PropertiesLoader in platform app
DDF-733  removed @author Javadoc per code review comment
DDF-733  removed use of obsolete CommonCallbackHandler class