Revert "allows add multiple submit buttons in "selectable" mode in SQLFORM.grid (with different decorate classes)"

This reverts commit 7055072ced1cc46c582257863761839e3b375700.
allows add multiple submit buttons in "selectable" mode in SQLFORM.grid (with different decorate css classes)
Merge branch 'feature/multiple_submit_buttons_in_grid' into develop