More structural parts in Early career mode.

[Whirligig Girl]

To encourage fun and more interesting building early on, I think some more structural part ought to be included in the first tech node.

Stack Tri-Coupler

Stack Bi-Coupler

Stack Quad-Coupler

Girder-1.25m Adaptor

Basic Ladder

Radial Stack Node

Cubic Octagonal Strut

Octagonal Strut (else the name of the Cubic Octagonal Strut makes no sense)

This idea came when I was playing 0.13.3 and 0.7.3 yesterday and remembered how fun the Stack Tri-Coupler was, and noticed that the Stack Tri-Coupler has no use by the time it's unlocked, because you probably have 2.5 meter rocket parts at that point.

[NecroBones]

I think definitely the bi/tri/quad stack couplers should be early parts. We should be getting used to parallel stacks of 1.25m parts before getting heavily into 2.5m. I forget how early they can be unlocked now though.