Beta 28 - rounded tile edges etc

Beta version 28 released

This version continues the bugfixing and polishing after the great graphics upgrade. This version brings an improved version of rounded tile edges. And a lot of minor glitches with 3D graphics has been fixed. The settings dialog now has a slider to adjust slope tint effect, which helps to tell sunny southern slopes from the shadowy northers slopes. (Yes, that matters for agriculture, crops grow better if they get more sunlight, also snow tends to thaw faster on the sunny side of a hill)