Simplify padding rules for SDG selector

Now the padding is only applied in two places (administration forms) so
we can apply it just there instead of applying it everywhere and then
removing it in most places. We're using the `column` class here because
it's what's used in the rest of the fields of these forms and because we
haven't defined (yet) general margin/padding rules for the
administration views.

app/assets/stylesheets/budgets/investments/form.scss

@@ -35,11 +35,6 @@
     @include grid-column-gutter;
   }
 
-  .sdg-related-list-selector {
-    padding-left: 0;
-    padding-right: 0;
-  }
-
   [type="submit"] {
     @include regular-button;
     font-size: map-get($button-sizes, large);

app/assets/stylesheets/debates/form.scss

@@ -5,9 +5,4 @@
     @include grid-row-nest;
     @include grid-column-gutter;
   }
-
-  .sdg-related-list-selector {
-    padding-left: 0;
-    padding-right: 0;
-  }
 }

app/assets/stylesheets/proposals/form.scss

@@ -5,10 +5,5 @@
     @include grid-row-nest;
     @include grid-column-gutter;
   }
-
-  .sdg-related-list-selector {
-    padding-left: 0;
-    padding-right: 0;
-  }
 }
 

app/assets/stylesheets/sdg/related_list_selector.scss

@@ -1,5 +1,4 @@
 .sdg-related-list-selector {
-  @include grid-column-gutter;
   clear: both;
 
   > legend {

app/assets/stylesheets/sdg_management/relations/edit.scss

@@ -1,6 +0,0 @@
-.sdg-relations-edit {
-
-  .sdg-related-list-selector {
-    padding: 0;
-  }
-}

app/views/admin/legislation/processes/_form.html.erb

@@ -187,8 +187,10 @@
   </div>
 
   <div class="row">
+    <div class="small-12 column">
       <%= render SDG::RelatedListSelectorComponent.new(f) %>
     </div>
+  </div>
 
   <div class="row">
     <div class="small-12 medium-3 column clear end">

app/views/admin/poll/polls/_form.html.erb

@@ -56,8 +56,10 @@
   </div>
 
   <div class="row">
+    <div class="small-12 column">
       <%= render SDG::RelatedListSelectorComponent.new(f) %>
     </div>
+  </div>
 
   <div class="row">
     <div class="clear">