Remove any remaining issues preventing us from support 'edge' browsers

[jstclair]

[jstclair]

Found a solution for the selection border issues that is widely-supported - woot! CSS Outline

Just requires a single line in the SelectionViews createElement:

function createElement(document) {
    var elem = createElem(document, 'div', 'editable-cell-selection');

    elem.tabIndex = -1;
    elem.style.backgroundColor = 'rgba(245, 142, 00, 0.15)';
    elem.style.outline = '1px solid #86bae8';

    return elem;
}