fpspreadsheet: Add code for detection of date/time cells which are incorrectly written as float by Open/LibreOffice. Implement conditional number formats for all number types (sometimes falsely assigned). Reactivate ignored date test cases for ods-1899, pass. 1904 date mode still faulty, not clear if this will ever pass the test.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3133 8e941d3f-bd1b-0410-a28a-d453659cc2b4