Add SunPy map support to solpolpy

[jmbhughes]

solpolpy will benefit with the use of Sunpy maps in addition to NDCubes for dataset like CATE for plotting and subsequent analysis. This will be good to identify the Solar north and subsequently other components of solpolpy such as alpha matrix generation, estimation of pB, pB' etc can be done based on this. Moreover, maps are easy to work around using existing architecture of sunpy. Inclusion of Maps will also be useful to combine the field of views in the future from non-PUNCH datasets such as PROBA3, Metis, and CODEX.