fix(visualize): Unit bug fixed for tile generation

A value in seconds was subtracted from a date value that was in
milliseconds. This caused extra tiles to be generated. Fixes #244.

Additionally the extra tiles should not have _even been visible_. This
bug was due to the sorting algorithm that determined the order of tiles
in the DOM not taking into account entities' starting date. It now sorts
by offset, and then by entity start date when a conflict occurs.

src/app/d3Bindings/eventDistribution/tiles.js

@@ -296,13 +296,18 @@ angular
                     }
 
                     /**
-                     * Order tiles based on their date. This allows elements to be painted in the
-                     * DOM in the right order
+                     * Order tiles based on their offset date, and secondarily, their recorded date.
+                     * This allows elements to be painted in the DOM in the right order
                      * @param tileA
                      * @param tileB
                      */
                     sortTiles(tileA, tileB) {
-                        return tileA.offset - tileB.offset;
+                        let delta = tileA.offset - tileB.offset;
+                        if (delta === 0) {
+                            return tileA.source.recordedDateMilliseconds - tileB.source.recordedDateMilliseconds;
+                        }
+
+                        return delta;
                     }
 
                     /**
@@ -324,7 +329,9 @@ angular
                         // round down to the lower unit of time, determined by `tileSizeSeconds`
                         var niceLow = roundDate.floor(idealTileSizeSeconds, low),
                         // subtract a 'tile' otherwise we generate one too many
-                            niceHigh = +(new Date(+roundDate.ceil(idealTileSizeSeconds, high) - idealTileSizeSeconds)),
+                            niceHigh = +(new Date(
+                                    +roundDate.ceil(idealTileSizeSeconds, high) - (idealTileSizeSeconds * msInS)
+                                )),
                             offset = +niceLow;
 
                         // use d3's in built range functionality to generate steps