Add ability to create a generic pipeline interface

[donaldcampbelljr]

Add ability to create a generic pipeline interface by using:

looper init -p or looper init --pipeline

close #327

[nsheff]

maybe --piface instead of --pipeline ?

[donaldcampbelljr]

maybe --piface instead of --pipeline ?

Yeah. Good catch. I'll make that change.

[donaldcampbelljr]

Also adding message to let user know the generic piface was successfully created.