Option for setting up --display-index

[rfrench3]

Setting the display index by simply having a number field could confuse users greatly, and it should be done with a clear dedicated interface.

[rfrench3]

I have decided that for the foreseeable future, an entire dedicated window for one specific feature is out of scope. Instead of a window, I may end up implementing it by telling users how to figure out what number to use by checking the system settings.