Rename muttrc variable

fix: `head` incompatibility between GNU and macOS

Replace head -n-1 with POSIX-compatible sed '$d'

chore: fix typo in README.md

The GNU-specific head -n-1 syntax causes errors on macOS/BSD systems.
Replaced with sed '$d' which is POSIX-compatible and achieves the same
result of removing the last line.

Added Bauhaus university weimar

$message_cachedir has been renamed to $message_cache_dir:
https://neomutt.org/guide/reference.html#3-244-%C2%A0message_cache_dir

Fix unary operator expected error

On my system running any `mw` command after a fresh install from the AUR, I get:

```
/usr/bin/mw: line 37: [: 1.5: unary operator expected
```

Now the script doesn't error per-se but it does set the `master` and `slave`
variables to wrong values. I'm also not sure how this wasn't raised before;
maybe that's a new bash version thing? I'm on 5.2.37.

Anyway I faffed around trying to fix this, in particular with the `-gt` operator
but it turned out that properly comparing float numbers is a pain in the butt in
bash. I found solutions using `bc` which I thought were weird.

To keep things simple I ended up doing a little substitution on the dot `.`
character and turned these nasty floats into integers, along with using the
`-gt` operator which did the trick on my system. May be unorthodox so feedback
is more than welcome.

Thank you for the great software by the way, lots of gratitude for your work.

This reverts commit 883e570d6d.

No mailsync with locked GPG key in non-interactive shells

Add goimapnotify for push notifications

fix(mailsync): delimit notification text from flags

Fix notify-send not coming through with goimapnotify

fix -P option description formatting in mw.1

Fix notifications for mails with multiline subject

Fix usages of mail/mails

Fixes text being interpreted as flags when it starts with a dash.
Try sending yourself a letter with subject starting with '-'.
E.g. if subject is '-10%' fixes error:
> Unknown option -10%

Signed-off-by: Jonas Dujava <jonas.dujava@gmail.com>

Signed-off-by: Jonas Dujava <jonas.dujava@gmail.com>

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.