Have the ability to add more than one part at a time to custom categories

[bigyihsuan]

SO I was playing KSP 0.90 this weekend, and I was having quite a bit of frustration at how adding parts to custom categories/sub-categories works. You have to repeat 3 steps for every part, and it gets really tiring when you're adding many parts at once.

A good way to eliminate this is to add a "Add Parts" button when you are in a subcategory that opens up a window that says to select the parts.

In this "Part Selection" mode, any parts you click on in the menus will be highlighted and be added to the selected subcategory when you click on the confirm button.

[Anquietas314]

Somewhat related: the subsystems interface could do with a bit of improvement for custom categories too. As it is (as far as I can tell) you can't change the category a system is stored in.