Support PrestaShop v8

[sinukaarel]

Is your feature request related to a problem? Please describe.
Prestashop is evolving and so should our plugin. Prestashop is now v8 and has received quite noticeable improvements. We should test our plugin and assess if it works with the newest versions.

Describe the solution you'd like
The features that the module has currently should also work in the latest version. I have tested that the module can be installed and is displayed in the admin panel, but validating credentials failed with a 500 error. Probably more places fail due to the major version upgrade.

Describe alternatives you've considered
There are probably no alternatives as we should aim to support also those who have upgraded their shop or are new shop owners with the latest version.

Additional context

• This is a nice blog post to understand the v1.7->8.0 upgrade.
• Enabling debug mode helps to catch errors
• List of core changes are listed here