Update code to be compatible with Joomla 4.0

[garstud]

Change code and deprecated fucntions to be able to run under Joomla 4.0.

[garstud]

I will surely need some help to perform various tests on Joomla 4.
So if you want to help us by testing JDump on Joomla 4, let us know. thank you in advance ;)

[garstud]

I just did a first simple test: install JDump v1.3.2 on a Joomla 4 Beta 5!
Results:

Fatal error: Cannot redeclare dump() (previously declared in C:\laragon\www\joomla40\libraries\vendor\symfony\
var-dumper\Resources\functions\dump.php:18) in C:\laragon\www\joomla40\plugins\system\dump\dump.php on line 97

So firstly, we have a conflict with the symfony Dump which is built into the Joomla framework!

We have 2 solutions:
1- integrate the notion of namespace in JDump to resolve the conflict.
2- rename our function "dump()" ... to "jdump()" for example?

Do you have any other ideas?

[garstud]

Secondly, once the namespace problem is resolved, many classes are obsolete, even very obsolete (JRequest!?). I start a cleaning based on https://api.joomla.fr/jplatform/deprecated.html