Settings option to create single-frame video annotations by default

[mzur]

Add a settings option to the video annotation tool to automatically finish new annotations after the first frame. If the option is active, the additional control buttons to finish or track an annotation should be hidden (or disabled?) from the UI.

[mzur]

The buttons to finish a pending video annotations are defined like this. These should no longer be shown when the settings option is active. When a new annotation is drawn extendPendingAnnotation() is called. If the new settings option is active, this could be immediately followed by calling finishDrawAnnotation().

The settings tab is here and here. The settings are stored here. The settings tab is described in this manual article.

[mzur]

When this new option is active, a mechanism to prevent double-click point annotations also has to be active (see #491 for the image annotation tool).