Add new environmental constraints

[rs028]

A procedure to add new environmental constraints. For example:

• rate coefficients typically depend on TEMP and/or PRESS (and sometimes on BLHEIGHT and DILUTE). Some processes can be added to the mechanism file that depend on another variable (eg, aerosol surface area, or something else currently not in the model or the mechanism), which should be possible to constrain.
• constraining latitude and longitude (eg, the model "is" on a ship or a plane).

One possibile solution is to put the constraint file in the environmentConstraints directory and add the corresponding line to modelConfiguration/environmentVariables.config.

[spco]

#157 has worked towards this, it's still not there yet though.

[rs028]

#432 show the procedure to add a new variable manually.