add API error handling facility

src/store/handleApiError.js

+export default function handleApiError (vm, err, message) {
+  if (err.response) {
+    vm.$log.error(err.response.status + ' ' + err.response.statusText)
+    vm.$log.error(err.response)
+    let msg = 'Error: '
+    if (message) {
+      msg += message
+    }
+    msg += '\n\n'
+    msg += 'Status code: ' + err.response.status + ' ' + err.response.statusText
+    alert(msg)
+  } else {
+    vm.$log.error(err)
+    if (message) {
+      alert('Error: ' + message + '\nInspect the console for more details.')
+    } else {
+      alert('Unspecified error. Inspect the console for details.')
+    }
+  }
+}