split UITrack.js into StaticTrack.js and GridTrack.js.

let's try to keep things strictly one class per file, unless the class
is not used anywhere outside of a file

index.html

@@ -26,7 +26,8 @@
     <script type="text/javascript" src="js/SequenceTrack.js"></script>
     <script type="text/javascript" src="js/Layout.js"></script>
     <script type="text/javascript" src="js/FeatureTrack.js"></script>
-    <script type="text/javascript" src="js/UITracks.js"></script>
+    <script type="text/javascript" src="js/StaticTrack.js"></script>
+    <script type="text/javascript" src="js/GridTrack.js"></script>
     <script type="text/javascript" src="js/ImageTrack.js"></script>
     <script type="text/javascript" src="js/GenomeView.js"></script>
     <script type="text/javascript" src="js/touchJBrowse.js"></script>

js/GridTrack.js

@@ -0,0 +1,18 @@
+//This track is for drawing the vertical gridlines
+
+function GridTrack(name) {
+    Track.call(this, name, name, true, function() {});
+}
+
+GridTrack.prototype = new Track("");
+
+GridTrack.prototype.fillBlock = function(blockIndex, block,
+                                         leftBlock, rightBlock,
+                                         leftBase, rightBase, scale,
+                                         padding, stripeWidth) {
+    var gridline = document.createElement("div");
+    gridline.className = "gridline";
+    gridline.style.cssText = "left: 0%; width: 0px;";
+    block.appendChild(gridline);
+    this.heightUpdate(100, blockIndex);
+};

js/StaticTrack.js

@@ -0,0 +1,23 @@
+//This track is for (e.g.) position and sequence information that should
+//always stay visible at the top of the view
+
+function StaticTrack(name, labelClass, posHeight) {
+    Track.call(this, name, name, true, function() {});
+    this.labelClass = labelClass;
+    this.posHeight = posHeight;
+    this.height = posHeight;
+}
+
+StaticTrack.prototype = new Track("");
+
+StaticTrack.prototype.fillBlock = function(blockIndex, block,
+                                           leftBlock, rightBlock,
+					   leftBase, rightBase, scale,
+					   padding, stripeWidth) {
+    var posLabel = document.createElement("div");
+    posLabel.className = this.labelClass;
+    posLabel.appendChild(document.createTextNode(Util.addCommas(leftBase)));
+    posLabel.style.top = "0px";// y + "px";
+    block.appendChild(posLabel);
+    this.heightUpdate(this.posHeight, blockIndex);
+};