Delete events should animate when played (#5919)

Same as PR #5640, except for the addition of a parameter in the JSON to turn this on or off.  While one would normally want animations/sounds on (e.g. undo/redo stack) sometimes they'd be annoying (e.g. events from realtime collaborators).

tests/mocha/event_test.js

@@ -469,6 +469,7 @@ suite('Events', function() {
             'x': 0,
             'y': 0,
           },
+          ui: true,
         }),
       },
       {
@@ -488,6 +489,7 @@ suite('Events', function() {
             'x': 0,
             'y': 0,
           },
+          ui: true,
           recordUndo: false,
         }),
       },
@@ -509,6 +511,7 @@ suite('Events', function() {
             'x': 0,
             'y': 0,
           },
+          ui: true,
         }),
       },
       {
@@ -529,6 +532,7 @@ suite('Events', function() {
             'x': 0,
             'y': 0,
           },
+          ui: true,
           recordUndo: false,
         }),
       },