fpspreadsheet: Building a number format list which allows to drop most of the restrictions of the previous versions like number of decimal places. New number format "nfCustom" which passes the format string directly to the file. 

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3044 8e941d3f-bd1b-0410-a28a-d453659cc2b4