Environment variables for default port and bind address

[Radical-Egg]

Hi,

There is not an open issue for this but I ran into an issue where I could not change the default port or bind address for snappass. In my case I installed via pip and wanted to bind snappass to 127.0.0.1 as I am planning to use a reverse proxy to reach the app. Is it possible to add the following two environment variables?

BIND_ADDRESS = 127.0.0.1 PORT = 6000

I tested that with no environment variables set, the defaults of 0.0.0.0:5000 are set and working. Given the following variables

BIND_ADDRESS = 127.0.0.1
PORT = 6000
HOST_OVERIDE = example.com

I can reach the app and links are generated with the appropriate URL.

ps. This is my first time submitting a PR, I apologize if I am missing anything.

Thanks all!