CLI refactor (#642)

* Initial refactoring of cli.py

* Renamed cli_help

* Refactored all cli commands

* Dropped support for 3.7

* Added test for export with --min-size

* Version bump

* Fixed python version

cli.py

@@ -12,7 +12,7 @@
     
 """
 
-from osxphotos.cli import cli
+from osxphotos.cli.cli import cli_main
 
 if __name__ == "__main__":
-    cli()
+    cli_main()