[ENHANCEMENT] Fix show for AbstractBlockSparseArray with unconvential type parameter orderings

[mtfishman]

I noticed that the show method introduced in #42 assumes the AbstractBlockSparseArray being printed has a certain type parameter ordering when printing the type, i.e. it assumes it is {eltype,ndims,blocktype,...}. We should constrain that part of the code logic to BlockSparseArray, and for other AbstractBlockSparseArrays print the entire type by default and expect them to define their own show method if they want more compact printing.