Major cleanup of many icons (started as a simple effort to tweak libedit and modedit icons)
Ref: https://lists.launchpad.net/kicad-developers/msg32860.html
* Each application icon has been updated
* Consolidated icon "modifiers" across many icons
* Replaced confusing arrows with "load" and "save" icons
* Slight code updates to reference correct icons
* Consolidate multiple representations of single icon type(s)
Seth Hillbrand
Oliver
Fabrizio Tappero