// Check if entire rows are selected. We call the selectedRows() method here not only for simplicity reasons but also because it distinguishes between
// "an entire row is selected" and "all cells of a row are selected", the former is e.g. the case when the row number is clicked, the latter when all cells
// are selected manually. This is an important distinction (especially when a table has only one column!) to match the users' expectations. Also never
// delete records when the backspace key was pressed.