Icon Request: Expand All / Collapse All

[edwardsdesign]

These icons would be useful to represent expand or collapse all items that have been grouped by parent or in an accordion.

[davegandy]

Will be done as a part of #675.

[josdejong]

I'm looking around for icons 'Expand all" and "Collapse all" to expand/collapse all items in an hierarchic tree (like a document structure) but can't find anything that comes close.

This is what I'm currently using, which is self made, but I would love to use font-awesome instead:

Any suggestions?