Add link to toggle column scrolling in board view

assets/css/src/board.css

@@ -113,9 +113,12 @@ a.board-swimlane-toggle:focus {
 }
 
 .board-task-list {
+    min-height: 60px
+}
+
+.board-task-list-compact {
     max-height: 90vh;
     overflow-y: auto;
-    min-height: 60px
 }
 
 .board-task-list .task-board:last-child {

assets/js/src/BoardVerticalScrolling.js

@@ -0,0 +1,53 @@
+Kanboard.BoardVerticalScrolling = function(app) {
+    this.app = app;
+};
+
+Kanboard.BoardVerticalScrolling.prototype.execute = function() {
+    if (this.app.hasId("board")) {
+        this.render();
+    }
+};
+
+Kanboard.BoardVerticalScrolling.prototype.listen = function() {
+    var self = this;
+
+    $(document).on('click', ".filter-vert-toggle-collapse", function(e) {
+        e.preventDefault();
+        self.toggle();
+    });
+};
+
+Kanboard.BoardVerticalScrolling.prototype.onBoardRendered = function() {
+    this.render();
+};
+
+Kanboard.BoardVerticalScrolling.prototype.toggle = function() {
+    var self = this;
+    var scrolling = localStorage.getItem("vertical_scroll") || 1;
+    localStorage.setItem("vertical_scroll", scrolling == 0 ? 1 : 0);
+
+    var task_lists = $(".board-task-list");
+    task_lists.each(function() {
+        // clear min-height so that it can be properly recalculated
+        $(this).css("min-height", "");
+    });
+    this.render();
+
+    // set up drag and drop again (resets min-height)
+    self.app.get("BoardDragAndDrop").dragAndDrop();
+};
+
+Kanboard.BoardVerticalScrolling.prototype.render = function() {
+    if (localStorage.getItem("vertical_scroll") == 0) {
+        $(".filter-vert-expand").show();
+        $(".filter-vert-collapse").hide();
+
+        $("#board td .board-task-list").addClass("board-task-list-compact");
+    }
+    else {
+        $(".filter-vert-expand").hide();
+        $(".filter-vert-collapse").show();
+
+        $("#board td .board-task-list").removeClass("board-task-list-compact");
+    }
+};