rename pillowtop.utils.import_pillows to pillowtop.get_all_pillows

I'm trying to start thinking about designing APIs with how they're used from the outside in mind, instead of how they're implemented. Was using this for something else, and `from pillowtop.utils import import_pillows` sounds like this scary private thing, whereas `from pillowtop import get_all_pillows` is where I'd look if what I wanted to do was get all the pillows that pillowtop knows about.