Adding more diagnostics default output to pkg/icefront?

[MPoinelli]

I am currently working on a set-up that uses the combination of icefront and shelfice to model ice-ocean interactions in ice rifts, where heat/salt fluxes along rift sidewalls are important in the rift circulation (e.g. Khazendar 2003, JGR).

At the moment, the icefront package only returns ICFfwFlx and ICFhtFlx as default output diagnostics. If worth it, I can work on including a further set of diagnostic in the default output list. In my work I only use ICFtendS and ICFtendT but I am open to suggestions for what else to include. The edits should be fairly straightforward.

Also, a minor comment/issue. After chatting with @owang01, I realized that in order to compare melt rate from vertical and horizontal ice-ocean interfaces, one needs to take into account the ratio between horizontal and vertical grid spacing if these are different. This is different from what happens in ECCO, where the ice front flux are scaled with the area ratio by default.
As this logical step is not immediate, I could include a simple note somewhere. As of now, I was thinking to just add some notes in what seems to be a small description of the pkg in icefront_description.tex . Hints on where to document are, of course, more than welcome.