Extract mailadress to .env file

[lodewiges]

Fixes #136
This PR extracts all the emailadresses to the .env file
It also changes to the default mail adres for archive notifications
and the email adres in the templates of unavailable mailadress template to be inline with bounced emails template.

before merging the .env files should be changed on the server

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (fbf1070) to head (84b5ede).
Report is 1 commits behind head on staging.

Additional details and impacted files

@@           Coverage Diff            @@
##           staging     #460   +/-   ##
========================================
  Coverage    99.92%   99.92%           
========================================
  Files          207      207           
  Lines         2733     2733           
========================================
  Hits          2731     2731           
  Misses           2        2           

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[DrumsnChocolate]

I've only read through the code, I have not tested this locally