fpspreadsheet: Add currency test cases to ReadString tests for biff8 and ods. Rename ReadDate tests to always show the datemode in the test name. Rename test files "testbiff8.xls" and "testodf.ods" to show datemode (1904) in file name (--> testbiff8_1904.xls, testodf_1904.ods)

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3198 8e941d3f-bd1b-0410-a28a-d453659cc2b4