Silo graphs and bug fixes

Added ability to show graph for storage silos. This required having a generalized graph dialog instead of being part of the industry. Now clicking the graph button will pop up a new dialog with the graph. This comes with a minor slowdown at the simulation speed at all times. This is because now I need to generate the graph data for the silos also. But this should be quite cheap.

I was incorrectly generating errors for tracks that were straight in 2D but had high curvature up or down as having too high of a curvature. Instead I should have been checking the 2D curvature instead of the 3D curvature.

I was also failing to detect when slopes were too steep. This is because I used to have only the absolute value of the slope. However, I changed the physics to use signed slopes, but didn't update my error checking code.

Fixed quest text that was incorrectly referring to the player's gender when it should be gender neutral.

Lots of internal refactoring that doesn't affect the player (Hopefully, unless I introduced bugs).