[FR] Add ability to add / remove / move spacers

[leevigraham]

It would be great to add / remove / move spacer tiles.

http://css-tricks.com/snippets/html/add-spaces-to-dock-in-os-x/

[kcrawford]

Adding is implemented in master and will be part of the the next release.

dockutil --add '' --type spacer --section apps --after Safari

I'm not sure how to implement move and remove since spacers don't have a label.

I could implement remove all spacers.

[kcrawford]

Implemented removal of all spacer tiles in master

dockutil --remove spacer-tiles

If you need moving of spacer tiles, please open a new issue. Thanks.