Motion animation export: a study or a joint drive as an animated GIF (#1680)

Thanks @SychPL.

assets/locales/en.json

@@ -92,6 +92,7 @@
   "Enable rule": "Enable rule",
   "Enabled": "Enabled",
   "Explode": "Explode",
+  "Export Animation…": "Export Animation…",
   "Export Current View as DXF": "Export Current View as DXF",
   "Export Current View as DXF…": "Export Current View as DXF…",
   "Export DXF…": "Export DXF…",
@@ -211,6 +212,7 @@
   "Round": "Round",
   "Rule": "Rule",
   "Save Rule": "Save Rule",
+  "Save the study as an animated GIF, seen as the viewport shows it": "Save the study as an animated GIF, seen as the viewport shows it",
   "Saved preview. Geometry is being checked before editing.": "Saved preview. Geometry is being checked before editing.",
   "Scale factor": "Scale factor",
   "Search": "Search",
@@ -426,6 +428,7 @@
   "cmd.model_threads": "List Threads",
   "cmd.motion_delete": "Delete Motion Study",
   "cmd.motion_export": "Export Motion Study",
+  "cmd.motion_export_animation": "Export Motion Animation",
   "cmd.motion_list": "List Motion Studies",
   "cmd.motion_play": "Play Motion Study",
   "cmd.motion_study": "Motion Study",