feat(timeline): add keyboard and scroll panning support

Enable horizontal scroll/swipe panning and keyboard navigation
(arrow keys to pan, +/- to zoom) using vis-timeline's built-in options.
Vertical scroll still zooms as before. Supersedes ActivityWatch#535.

Closes ActivityWatch#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 zoom, swipe/horizontal-scroll to pan, arrow keys to navigate
 
   div(v-if="buckets !== null")
     div(style="clear: both")

src/visualizations/VisTimeline.vue

@@ -102,6 +102,12 @@ export default {
           overflowMethod: 'flip',
           delay: 0,
         },
+        // Keyboard & scroll navigation (see #629)
+        horizontalScroll: true, // horizontal scroll/swipe pans the timeline
+        keyboard: {
+          enabled: true,
+          speed: { x: 10, y: 0, zoom: 0.02 },
+        },
       },
       editingEvent: null,
       editingEventBucket: null,