message: Fix header counters to correctly handle zero
  Currently if you set the value to zero the counter is not displayed.
diff: @@ -122,7 +122,9 @@ module.exports = React.createClass({
  const severity = ev.getContent().severity || "normal";
  const stateKey = ev.getStateKey();
  - if (title && value && severity) {
  + // We want a non-empty title but can accept falsey values (e.g.
  + // zero)
  + if (title && value !== undefined) {
  counters.push({
  "title": title,
  "value": value,
  