The iconopt folder is not cleaned on build

If you rename iconraw files and rebuild, the icon is now included with both the old and new names. This occurs because their is no grunt task to clean the iconopt folder prior to running the optimization task.

Locate the Grunt configuration and the optimization task that writes to the iconopt folder. Check the build sequence for the missing cleanup step, then verify that rebuilding after renaming an iconraw file leaves only the current optimized icon names in iconopt.

Written by the indexing model from the issue text.