Fix crontab backslash

[Anuril]

This was a fun one 😄

This fixes #4329 and some other issues with crontabs that were not yet found.

1. The bash function read removed the backslash when reading the $USER_DATA/cron.conf file because -r wasn't used - so json_decode never received the string with \.
2. If json_decode in web/list/cron/index.php would have received it, it would've been buggy, as json_decode can't deal with single backslashes, so we have to manually escape the backslashes.
3. The same issue plagued the edit functionality so we do the same thing in /web/edit/cron/index.php

I also noticed that the same thing happened when I wanted to use this crontab line:
/usr/bin/find /home/testuser/test/ -type f -exec echo "Files: "ls {} >> /home/testuser/test/log.log \;

And that issue was with double quotes.

EDIT: This also caused to not create the cron tab entries in the correct way, as func/main.sh also didn't use the -r flag with read.

I also just noticed that there might be an issue when upgrading when suddenly the cronjobs in $USER_DATA/cron.conf are in a wrong format, which breaks the display of the list. I'll create a script to fix that.

EDIT2: Fixed all the parsing issues with quotes and backslashes and all other characters by converting the command string to base64 and storing it that way.