Change Build Aid window to show the duration even if the vessel has no crew capacity

[taraniselsu]

Thought of the idea after reading:
http://forum.kerbalspaceprogram.com/index.php?/topic/96402-105-procedural-parts-parts-the-way-you-want-em-v1111-dec-16/&do=findComment&comment=2304896

The Build Aid window could show how many days the current supplies would last for 1 Kerbal, even if there are no crewable parts on the vessel. Might make unmanned resupply missions easier to build.