Allow grass curing, leaf-on/off, and other calculated conditions to be set manually

[jordan-evens]

Right now time of year and location is used for curing and green-up.

Should be able to override any and/or all calculated values with any of:

• a single value for entire run
• a start-up value to be used as the initial condition, and then use the existing equations to calculate the difference to change that by
• a list of individual values to be used hourly