Add header link for host donut chart

Add link on the header that opens the list that the host donut
chart in the tactical overview represents considering the active
filters.

Author: jrauh01

library/Icingadb/Widget/HostSummaryDonut.php

@@ -66,12 +66,24 @@ protected function assembleFooter(BaseHtmlElement $footer)
 
     protected function assembleHeader(BaseHtmlElement $header)
     {
+        $filter = Filter::all();
+
+        if ($this->hasBaseFilter()) {
+            $filter->add($this->getBaseFilter());
+        }
+
+        $attributes = Attributes::create(['href' => Links::hosts()->setFilter($filter)]);
+
         $header->addHtml(
-            new HtmlElement('h2', null, Text::create(t('Hosts'))),
-            new HtmlElement('span', Attributes::create(['class' => 'meta']), TemplateString::create(
-                t('{{#total}}Total{{/total}} %d'),
-                ['total' => new HtmlElement('span')],
-                (int) $this->summary->hosts_total
+            new HtmlElement('a', $attributes, new HtmlElement('h2', null, Text::create(t('Hosts')))),
+            new HtmlElement('a', $attributes, new HtmlElement(
+                'span',
+                Attributes::create(['class' => 'meta']),
+                TemplateString::create(
+                    t('{{#total}}Total{{/total}} %d'),
+                    ['total' => new HtmlElement('span')],
+                    (int) $this->summary->hosts_total
+                )
             ))
         );
     }