Add flag to use raw pulse input numbers

[ollien]

As it stands, using pswitch o n or pswitch i n will use pulse's raw indexes. However, in some scenarios, it is desirable to use the indexes that pswitch generates when using pswitch o or pswitch i. A flag should be added to utilize the current behavior, but make the latter behavior default.

Note that this is the cause of

Traceback (most recent call last):
  File "/home/nick/.local/bin/pswitch", line 11, in <module>
    sys.exit(main())
  File "/home/nick/.local/lib/python3.6/site-packages/pswitch/__main__.py", line 82, in main
    sink_name = pulse.get_single_sink(sys.argv[2])["device_name"]
TypeError: 'NoneType' object is not subscriptable