add new theme: powerline-shell wrapper for fish

[leleliu008]

add new theme: powerline-shell wrapper for fish

[derekstavis]

Would you mind removing the -theme from the end of the filename? It's not necessary because the package type is defined by the package definition file.

[leleliu008]

@derekstavis can't remove the -theme from the end of the filename for the following reasons:

1. a package who is named powerline which type is plugin already exist. it is wrapped for powerline-status
2. my new package's type is theme, it is wrapped for powerline-shell

[bobthecow]

installing this theme sets fish keybindings to vi mode (and this persists even after removing the theme). this feels like … not the sort of thing a theme should do :)

[leleliu008]

@bobthecow I have removed the key_bindings.fish