init for min/max date/distance

public/js/app.js

@@ -2,6 +2,12 @@
 var WIDTH = 800;
 var HEIGHT = 600;
 
+var MAX_DISTANCE = 5;
+var MIN_DISTANCE = 0;
+
+var MIN_DATE = new Date('2016-1-1');
+var MAX_DATE = new Date('2017-1-1');
+
 d3.select('svg').style({
 	height: HEIGHT,
 	width: WIDTH