Pre-release v2.1.0a: non-conservative force calculation included in QGField

This pre-release is made for the sake of generating a zenodo code to be included in Lubis et al. (in prep). Functionality to compute the contribution of diabatic heating in the wave activity budget equation is included. See documentation of QGField.compute_lwa_and_barotropic_fluxes for details. A formal release will be made once the manuscript is finalized.