4 sprites by supermop:
http://devs.openttd.org/~frosch/ConvertRoad.png

Also needs equivalent changes to ogfx tram depot sprites as in OpenTTD extra grf: https://github.com/OpenTTD/OpenTTD/blob/master/media/extra_grf/tramtracks_bare_depot.png

[9:26pm] frosch123: it "just" needs copying of the sprites, and overdrawing of the tracks with blue pixels. nothing fancy, just work

This is to edit the existing ogfx sprite, not copy the openttd extra sprite.

• add 'tram' global toolbar icon
• add 'convert road' / 'convert tram' toolbar and cursor icons
• the 'convert rail' toolbar icon is included in sprites/png/gui/gui2x.png, but the equivalent 'convert road' / 'convert tram' icons are not provided at 2x yet, this looks inconsistent
• the first 2 icons in tram building toolbar are incorrect at 2x, sprites already exist in gui2x.png, use those
• adjust depot sprites

Done #34