Fix overhang issue and flat grid-joinment.

[Pytonballoon810]

Fix the Baseplate Issue described in #249

Rework of implementation in Commit 3e4d870

The fix also makes it such that the bin itself sits WAY better in the base. (it extends the bottom of the bin a slight bit (0.5mm) which is no problem.)

Fixes this overhang issue:

Before:
First closing layer:

Top seem layer:

From below:

Printed (here you can also see the flat intersection of the grid elements):

After:
First closing layer:

Top connection layer

From below:

Printed (no cleanup, deeper intersection for better base fitment):

[EmperorArthur]

Where are the numbers coming from? I see you comment about the 0.5mm change, but am not a fan of it being hard-coded. Similarly, dividing by a random constant seems strange.

[Pytonballoon810]

    translate([0, 0, BASE_HEIGHT-top_bottom_thickness])

Removing the -top_bottom_thickness moves the filling on top of the intersection of the modules. Dividing by some value moves it back down. I don't know the code well enough to know whether there is a variable suitable for that but I found my value to be very good for how it should look

Dividing the second value limits the height of the connection joint to a fraction of its original value.

In combination this means that the base is not filled and thus removing all those nasty overhangs you can't print properly.

I don't know why dividing by a constant would be a problem.

Also sorry if my solution is unconventional. This was my first time writing anything for openscad but as I use this project a lot I also wanted to contribute.