Order issues by label priority instead of id on board lists

app/assets/javascripts/boards/models/issue.js.es6

@@ -12,6 +12,10 @@ class Issue {
     obj.labels.forEach((label) => {
       this.labels.push(new Label(label));
     });
+
+    this.priority = this.labels.reduce((max, label) => {
+      return (label.priority < max) ? label.priority : max;
+    }, Infinity);
   }
 
   addLabel (label) {

app/assets/javascripts/boards/models/label.js.es6

@@ -4,5 +4,6 @@ class Label {
     this.title = obj.title;
     this.color = obj.color;
     this.description = obj.description;
+    this.priority = (obj.priority !== null) ? obj.priority : Infinity;
   }
 }

app/views/projects/boards/components/_card.html.haml

 %board-card{ "inline-template" => true,
-  "v-for" => "issue in issues | orderBy 'id' -1",
+  "v-for" => "issue in issues | orderBy ['priority', 'id']",
   ":issue" => "issue",
   ":issue-link-base" => "issueLinkBase",
   ":disabled" => "disabled",