Add var as marker to detect GetSection() call

[mahotilo]

For section with $section['always_process_values'] = true; it is useful to distinguish which function includes section.php at the moment. With this PR, if $GettingSection is set, it tells us that we are in GetSection() call (not in SectionTypes() or LoadSectionCssJs() ) and $sectionCurrentValues is really set with current section values.

Yes, I know your position about my attempts to use CS in a situation where it is much easier to make a normal plugin. But CS is so good as a rapid development tools. And I generally succeed at doing whatever I want in my section. But sometimes I think that, if $section['content'] was not an array but a function, it would be much easier to work with a config file, a Session and so on:)

[mahotilo]

BTW, about real estate in the editing panel. I use this little trick to hide some editing settings if they are disabled. This helps me to escape scrolling.

      // value 'telegram' --start
      'telegram' => array(
      'label' => $editor_lang['Use_Telegram'].' <i class="fa fa-paper-plane"></i>',
      'control_type' => 'checkbox',
      'attributes' => array(),
      'on' => array(
        'CustomSection:formElementsLoaded' => 'function(){$(this).trigger("change")}',
        'change' => 'function(){ 
            $c = $("[name = \'values[telegram_token]\']").closest(".editor-ctl-box");
            if ( $(this).val() == "1" ) { $c.show(); } else { $c.hide(); };
            $c = $("[name = \'values[telegram_chat_token]\']").closest(".editor-ctl-box");
            if ( $(this).val() == "1" ) { $c.show(); } else { $c.hide(); };
                        .................
         }',
      ),
    ),
    // value 'telegram' --end

[mahotilo]

Well. I have found that $current_section['attributes']['id'] can be used instead to detect the GetSection() call. So this PR can be cancelled.