fpspreadsheet: Add variant of the fpsgrid demo which does not require installation of the laz_fpspreadsheet_visual package. Fix incorrect centering of text in merged cells.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3565 8e941d3f-bd1b-0410-a28a-d453659cc2b4