Compatibility fixes for PHP 8.2

[s1shed]

This fixes various warnings and errors in PHP 8.2 and is intended to complement #282.

[infrastation]

Thank you, that's a large diff, please let me have some time to proof-read the changes.

[s1shed]

No problem, hopefully it's of use. :)

Just stumbled on this with PHP 8.2:

Deprecated: Function strftime() is deprecated in /racktables/wwwroot/inc/functions.php on line 6374

[infrastation]

That's a separate problem and it will take a separate solution (replace strptime() and strftime() with something and something else), but thank you for bringing this up.

[andypost]

this functions are deprecated in 8.1.0

This function has been deprecated. Use date_parse_from_format() instead (for locale-independent parsing), or IntlDateFormatter::parse() (for locale-dependent parsing)

[BasvanH]

When is this going to be merged?