fpspreadsheet: In the unit tests, use the same methods for creating "soll" date/times and test format strings. --> No more biff-related regressions.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3078 8e941d3f-bd1b-0410-a28a-d453659cc2b4
fpspreadsheet: Restore excel2write demo forgotten in previous commit

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3079 8e941d3f-bd1b-0410-a28a-d453659cc2b4