Use local files when changing icon to blue

Make the script use the local version of the blue icons #593

N.B.: I did *not* replace the empty icon files with the actual blue icons. I think that those icon changes may be the commits that caused at least some of the [conflicts](https://groups.google.com/d/msg/anki-android/9D5PWloe-jg/h__a2Wwl86oJ) when merging develop into master. Maybe that merge should be tagged somehow? How exactly?

This also explicitly uses bash, just because i like to use the directory stack. Other ways (with plain sh) are possible.