include jubatus-type in filename

fix #709 

Jubatus's saves/loads file with like filename of `127.0.0.1_9199_jubatus_hoge.jubatus` now.
It confuses users "Which jubatus algorithm saves/loads this file?"

I think filenames should contains algorithm name to be like `127.0.0.1_9199_classifier_hoge.jubatus`

memo: Modification of document is needed too.