Add "Vertical" as a load direction

**Is your feature request related to a problem? Please describe.**
When adding a gravity loads, such as snow, to a sloped member the user has to resolve the load into the appropriate "Transverse" and "Axial" components and apply both.

**Describe the solution you'd like**
It'd be handy to have a third load direction, "Vertical", with the T and A components automatically resolved and applied to the member.

**Additional context**
Taking it a step further, perhaps there could be 4 load types: x-local, y-local, X-global & Y-global. Or "Axial", "Transverse", "Horizontal" & "Vertical" if you prefer.

No files, tests, or entry points are named. First locate the existing Axial and Transverse load handling in the VBA library, then trace how member loads are resolved; done means a Vertical direction automatically resolves and applies the appropriate components.

Written by the indexing model from the issue text.