Rename import.py, since import is a keyword

from sticker.import import cmd
                 ^
SyntaxError: invalid syntax

Fixes https://github.com/maunium/stickerpicker/issues/27.

setup.py

@@ -47,7 +47,7 @@ setuptools.setup(
         "Programming Language :: Python :: 3.8",
     ],
     entry_points={"console_scripts": [
-        "sticker-import=sticker.import:cmd",
+        "sticker-import=sticker.stickerimport:cmd",
         "sticker-pack=sticker.pack:cmd",
     ]},
 )