Fix redirections to empty tabs (#290)

Whenever href (url) attribute was omitted or had no value
the click action would do nothing. With no URLs defined and
`target="_blank"` attributes, which were recently added,
anchor tags now redirect users to new blank tabs (side effect).

This PR solves the issues by adding conditions
before applying `target="_blank"` or in some cases by
ommiting entire entities (e.g. the view_certificate button).

layouts/partials/cards/project.html

@@ -4,7 +4,7 @@
 >
   <div class="card mt-1">
     <div class="card">
-      <a class="card-header" href="{{ if .repo }}{{ .repo }}{{ else if .url }}{{ .url }}{{ else }}javascript:void(0){{ end }}" target="_blank">
+      <a class="card-header" href="{{ if .repo }}{{ .repo }}{{ else if .url }}{{ .url }}{{ else }}javascript:void(0){{ end }}" {{ if or .repo .url }}target="_blank"{{ end }}>
         <div>
           <div class="d-flex">
             {{ if .logo }}