Add the new 'modern' email templates

[LouiseBonnard]

Is your feature request related to a problem? Please describe:

At the time the module was coded, PrestaShop included only one default email template: the 'classic' email template. Since version 1.7.6, PrestaShop offers two default email templates - the 'classic' and the 'modern' - but here the late 'modern' template is not taken into account.

Currently, when a user has a 'modern' default email theme, the module states that his/her current email theme is 'classic'.

Describe the solution you'd like:

Keep the two frames, the first one to import a pack of templates and the second one to preview the current template, but make the second frame recognizes whether it is 'modern' or 'classic' and offers the right screenshot.

Describe alternatives you've considered:

If impossible, at least modify the wording in the second frame to erase the mentions of 'classic' or 'modern' and states only about the fact that it is the current template - with the right thumbnail but without specifying its name.