Implemented delete functionality

ADDED: deleteSelected() and itemsDelete() to do the clearing/deletion
ADDED: blankRow() to clear a row rather than remove it
ADDED: getColNameByIndex() - not used! Doh.
CHANGED: sortrows() now marries the data to rows before sort, and resplits
FIXED: getSelectedRowIndices() -> getSelectedIndices(), plus bugs
ADDED: Centralised empty string
ADDED: Delete button to harness, plus hookups