Add option to export parts seperately

[battlesquid]

• Add the ability to export the skyline towers, base, logo, name, and year text separately.
  • Skyline towers will need an additional thin base to keep them together
    • Maybe do the same for text

[battlesquid]

Another idea: instead of using a thin flat base, make it so that geometry is added underneath the towers can "slot" into base. For example, add a wedge underneath the towers, and cut out that wedge from the shape to allow it to slot in. This makes it easier to connect the separated pieces together. This "slot" feature should probably be toggleable, but I imagine it would help most users in assembling the skyline.