Moved proxy- and mint-URL to .env file

[GitHappens2Me]

This PR moves all hardcoded URLs ( https://api.routstr.com & https://mint.minibits.cash/Bitcoin ) to a new .env file.

I changed all occurrences of those URLs, so that the current value set in .env is used. I also added the current value as defaults, so without creating the .env file, nothing should change.

This enables anyone to run their own Proxy and Chat and connect them. Similiarly to what this Issue

[vercel]

@GitHappens2Me is attempting to deploy a commit to the evanyang's Team Team on Vercel.

A member of the Team first needs to authorize it.

[sh1ftred]

Hey, thanks a lot for the pr.
I've already made significant changes to this logic if you look at the staging branch. You've been making great prs overall, but I'll have to close this one without merging. :)
Please join our Chorus group to discuss new features and collabs!

[GitHappens2Me]

A bit late to the party here, sorry about that!
@sh1ftred Can you tell me where / how I can join the Chorus group.
I found a Routstr group on chorus.community but not sure if it is the right one / still the prefered way of communication.