feat(timeline): add keyboard and scroll panning support

Enable horizontal scroll panning, Ctrl+scroll zooming, and keyboard
navigation (arrow keys to pan, +/- to zoom) using vis-timeline's
built-in options. Previously only click-and-drag was available.

Closes #629

Author: TimeToBuildBob

src/views/Timeline.vue

@@ -55,7 +55,7 @@ div
               option(:value='1 * 60 * 60') 1+ hrs
               option(:value='2 * 60 * 60') 2+ hrs
   div(style="float: right; color: #999").d-inline-block.pt-3
-    | Drag to pan and scroll to zoom
+    | Scroll to pan, Ctrl+scroll to zoom, arrow keys to navigate
 
   div(v-if="buckets !== null")
     div(style="clear: both")

src/visualizations/VisTimeline.vue

@@ -102,6 +102,13 @@ export default {
           overflowMethod: 'flip',
           delay: 0,
         },
+        // Keyboard & scroll navigation (see #629)
+        horizontalScroll: true, // mouse wheel pans horizontally
+        zoomKey: 'ctrlKey', // Ctrl+scroll to zoom (instead of plain scroll)
+        keyboard: {
+          enabled: true,
+          speed: { x: 10, y: 0, zoom: 0.02 },
+        },
       },
       editingEvent: null,
       editingEventBucket: null,