Enable efloor+fingerslide options [3]

[danielsan80]

Hi Jamie,

I thought it would be useful to have both the efficient_floor and fingerslide options enabled together, but I noticed you had prevented this. I checked if there were any issues with allowing it, and it seems to work.

Maybe that difference-union-difference-union part should be refactored, but... one step at a time.

[danielsan80]

UPDATE: This issue was solved by @ostat in his project https://github.com/ostat/gridfinity_extended_openscad