fpspreadsheet: Row heights now can be saved to all biff versions. Add unit test case for row heights, ok. Bug fixed in BIFFExplorer with format detection.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3019 8e941d3f-bd1b-0410-a28a-d453659cc2b4
fpspreadsheet: the worksheetgrid can be edited again. Beginning to add some cell formatting to the demo.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3020 8e941d3f-bd1b-0410-a28a-d453659cc2b4