Toggling toolbar icons does not refresh

[colinmo]

While using Append and Prepend you can add buttons to a Toolbar and it refreshes, if you change an existing ToolbarItem and try to refresh, it does not. This is because toolbar.resetObjects first checks to see if the number of toolbar items has changed before doing any refreshing. Obviously if changing the image for an icon (for example toggling bookmark on/ off for a list) the number of items in the toolbar does not change.

To Reproduce:

1. Create a toolbar via widget.NewToolbar with any number of ToolbarItems with icons
2. Display the toolbar in a window/canvas/layout.
3. Programmatically change any of the ToolbarItems
4. Refresh the window/canvas/layout/toolbar
5. The icon does not change

Alter the code in toolbar.go to remove the changed-items-count test and the button changes.

Example code:

func toggleBookmark() {
	var index = isBookmarkedAt(dt.Format("2006-01-02"))
	if index == -1 {
		appPreferences.Bookmarks = append(appPreferences.Bookmarks, dt.Format("2006-01-02"))
		toolB.Items[8] = widget.NewToolbarAction(theme.ContentRemoveIcon(), toggleBookmark)
	} else {
		var mep = appPreferences.Bookmarks
		appPreferences.Bookmarks = append(mep[:index], mep[index+1:]...)
		toolB.Items[8] = widget.NewToolbarAction(theme.ContentAddIcon(), toggleBookmark)
	}
	sort.Strings(appPreferences.Bookmarks)
	bookmarksList.Refresh()
}

Device (please complete the following information):

• OS: Tested on Windows and MacOS
• Version: Windows 10, MacOS Catalina
• Go version: go1.13.5
• Fyne version: 1.4.3

[andydotxyz]

On develop for testing