Fixes #28. Move to use time_ave_util

[mathomp4]

Closes #28

This PR migrates the scripting to use time_ave_util.x which is much better at handling things like the cube-sphere and tripolar grids. @bena-nasa can probably tell more about why we should use it.

ETA: From @bena-nasa in #28:

Just some history on this. At some point, people said, now that we are producing files on things other than LL grids, the post-processing should support it. This included time_ave.x. Now since time_ave.x used GFIO, it could not be extended to support all files we produce and keep GFIO. I decided to create a new time_ave_util.x in MAPL starting from time_ave.x, but using the modern IO system that History and ExtData use so that if they support it, the utility can use it. I felt at the time for people's comfort I would keep the old code so people could be convinced that yes this does for Lat-Lon files produce the same answer. My hope was that Larry would test this and convert the scripts to use it, but he never did. In any case, this is what I intend to support and has all the same options (plus more) that the old time_ave.x has, so it should just be a drop-in replacement. time_ave.x should be considered no longer supported as I'm not supporting it, that's why write I wrote the new one and since Larry is retired, no one is.

NOTE: Keeping draft until someone like @sdrabenh or @Jcampbell-8 can try it out. I think it'll work...