Add support for overriding sponsor URL at event level (#399)

This allows for events to put in a specific URL for their sponsor, for event-level tracking.

Signed-off-by: Matt Stratton <matt.stratton@gmail.com>

Author: mattstratton

layouts/partials/sponsors.html

@@ -33,8 +33,14 @@ <h4 class="sponsor-cta">{{ $level.label }} Sponsors</h4>
 
             {{ if isset $.Site.Data.sponsors .id }}
 
+            {{ if .url }}
+              {{ $.Scratch.Set "SponsorURL" .url }}
+            {{ else }}
+              {{ $.Scratch.Set "SponsorURL" $s.url }}
+            {{ end }}
+
               <div class = "col-lg-1 col-md-2 col-4">
-                <a href = "{{ $s.url }}"><img src = "/img/sponsors/{{ .id }}.png" alt = "{{ $s.name }}" title = "{{ $s.name }}" class="img-fluid"></a>
+                <a href = "{{ $.Scratch.Get "SponsorURL" }}"><img src = "/img/sponsors/{{ .id }}.png" alt = "{{ $s.name }}" title = "{{ $s.name }}" class="img-fluid"></a>
               </div>{{ "<!-- close individual sponsor div-->" | safeHTML}}
             {{- end -}}
           {{- end -}}