Land Management: Don't return large objects/sets when we're not going to use them

[#70457564]
Land Management: Cache our surface patch list

... that way we don't have to search as hard to find the correct ones on
each step.

[#70457564]
Land management: Fix soil quality behavior

[#70782444]
Land Management: Bare soil should rapidly decrease soil quality

[#70782444]
Land management: New plant images

[#65235688]
Land Management: Use a simple linear gradient for the sky color

[#65235688]
Land Management: Update soil colors

[#65235688]
Land Management: Revert the zone label colors since those match the graph lines

[#65235688]
Land management: Fix a typo in the sky color generator

[#65235688]
Land management: Updated terrace color

[#65235688]
Land management: Adjust zone labels so they don't overlap with topsoil ever

[#65235688]
Land Management: Make sure to reset target soil quality when resetting the model

[#70782444]
Bump agentscript version to eliminate fuzziness on IE
Land Management: Use patchXY() instead of patch()

...  since we know our x,y values won't need wrapped/clamped.

[#70457564]
Land Management: Limit our redraw rate to 30 fps
Air pollution: Fix factory positioning in IE

[#77249566]
Water: Fix cursors so they work better in IE

[#63829380]
Water, Fracking: Fix model interaction bug in IE 9/10

[#63829380]
Climate, Land Management: Update years in UI/graphs to start in the current year

[#80461362]
Land management: Add graph key to model

[#80461116]