Removed load_contents parameter from FileInfo

FileInfo will now only load file metadata when initialized. This ensures
that FileInfo objects are created quickly and makes sure that file
contents can only be loaded via an explicit call to the load method.
FileInfo now supports optional interface to DataViews NdMappings
Added support for .view files (pickled DataViews) to filetypes
Casting lancet.__version__ to string for JSON serialization