muttrc: use XDG_CACHE_HOME in notmuch integration

Fixes `sh: 1: cannot create /home/<username>/.cache/mutt_terms:
Directory nonexistent`.

cleanup Makefile

fix: rename variables

Added `fz-juelich.de` domain

Fix escaping in message IDs from notmuch

Don't prompt for password, if the email address already has one stored.

Added direct link to Google App Password page for easier access

password. This is useful if you copy your .password-store
directory from one computer to another.

* OS variable was unused
* ifndef section is not needed since
  "make PREFIX=... MANPREFIX=..." overwrites
  whatever is set there
* notdir is a GNU specific function (not POSIX) and doesn't do
  anything in this case
* "sed -i" is not POSIX and pointless if pipes are used correctly
* the "if" block can be removed since "sed" can also be used to
  copy files to the destination.

According to:
  https://neomutt.org/guide/reference.html#3-380-%C2%A0realname
  https://neomutt.org/guide/reference.html#3-480-%C2%A0spoolfile

`+` was properly escaped but only once. `$` was not escaped at all.
This would result in messages with message IDs containing more than one
`+` or at least on `$` to not be shown after limiting.
`$` itself has to be escaped presumably for the shell. This results in
three prepended backslashes in the limit string and six in the config
file, as there backslashes themselves have to be escaped.

fix: reorder action

pipe password directly to pass

fix typo in set crypt_auto_sign

Update domains.csv

Update domains.csv

- also change slightly confusing naming for (re)inserting given
      passwords to pass store

exclude dovecot special folders fts-flatcurve/virtual

Add gettext dependency to README

gettext which provides the envsubst command is not installed on all distributions. Void for instance does not come with this, so I think it should be mentioned in the README.

Update domains.csv

Add highlighting for flagged emails

Forward email body as text

Switch msmtp log file to XDG_STATE_HOME

Made script more readable and redirected error