fixing bug #4758 : transform ImportReportManager class into a singleton
Bug #4727 : adding the possibility to define default date or/and hour for the date checker plug-in.
refactor the work of Cecile in order to keep the ImportReportManager thread-safe
Merge branch 'core-5.12.x' of github.com:Silverpeas/Silverpeas-Core into core-5.12.x