Load actions and filters only for the admin CPT list

The trouble is that this peace of code are ignored and not executed:

It is because there is no action with name edit-wt_whoisservers

From your code it seems that instead of calling WTRegisterCPTStuff() through an add_action, you can call it directly to load resources for the CPT list.

So, the following code

//Load stuffs for the CPT list
add_action( 'edit-wt_whoisservers', array($this, 'WTRegisterCPTStuff') );

can be replaced with something like this:

if ( 'wt_whoisservers' == get_current_screen()->id ) {    // 
    $this->WTRegisterCPTStuff();
 }

I hope this helps.