Make all the imports in sunpy.io.file_tools optional

I have made this in such a way that it will not fail until it tries to
read a file with an unsupported filetype and then it raises a nice error.
Change from 'fz' to 'ana' and put JP2 exception back.
Merge pull request #665 from Cadair/fix_io_imports

Make all the imports in sunpy.io.file_tools optional