checks for fConcGas input

[rs028]

• Temperature and Pressure for fConcGas() must be either one value or same number of values as rows in input data.

• Validate inputs for "UG" cases.

[rs028]

Same for fConcAq. Plus similar checks for the functions in physChem.R.

[rs028]

Repeated logic for handling molar mass arrays. Could be refactored into a helper function.