add parity support for buildings from streetmix import

[kfarr]

managed street should support buildings as well as legacy streetmix import

• suggest 0 width segment at start/end of street line - so it will not affect segment width sizing
• review current building alignment, double check if we need to change. https://github.com/3DStreet/3dstreet/issues/1047
• allow alignment of buildings along a line
• the line will be the property line
• suggest to have custom UI to allow for selecting popular building types, similar to streetmix