PR #943 updating Body, Part and Assembly icons

[pablogil]

Updating Body and Part new icons and suggesting a new Assembly icon as discussed in forum thread:
https://forum.freecadweb.org/viewtopic. ... a764e95d61

Also, merge it always after PR #916 (https://github.com/FreeCAD/FreeCAD/pull/916) because it has slight icon design updates.

Thanks

[pablogil]

Due to an error, the previous branch and PR modifications are no longer available, so I have created a new branch and new PR:
https://github.com/FreeCAD/FreeCAD/pull/965

Again, please, merge it after PR #916 (https://github.com/FreeCAD/FreeCAD/pull/916) because it has slight icon design updates to that PR.

Thanks