Fix deprecated argument order for "implode()"

Summary: Fixes T13428. In modern PHP, "implode()" should take the glue parameter first.

Test Plan:
Used the linter introduced in D20857 to identify affected callsites.

```
$ git grep -i implode | cut -d: -f1 | sort | uniq | xargs arc lint --output summary --never-apply-patches | grep -i glue
```

Maniphest Tasks: T13428

Differential Revision: https://secure.phabricator.com/D20858

src/applications/differential/lipsum/PhabricatorDifferentialRevisionTestDataGenerator.php

@@ -103,7 +103,7 @@ final class PhabricatorDifferentialRevisionTestDataGenerator
         $newcode2[] = $altcodearr[$randomlines_new[$c++]];
       }
     }
-    return implode($newcode2, "\n");
+    return implode("\n", $newcode2);
   }
 
 }

src/applications/people/view/PhabricatorUserCardView.php

@@ -38,7 +38,7 @@ final class PhabricatorUserCardView extends AphrontTagView {
     }
 
     return array(
-      'class' => implode($classes, ' '),
+      'class' => implode(' ', $classes),
     );
   }
 

src/applications/project/view/PhabricatorProjectCardView.php

@@ -36,7 +36,7 @@ final class PhabricatorProjectCardView extends AphrontTagView {
     $classes[] = 'project-card-'.$color;
 
     return array(
-      'class' => implode($classes, ' '),
+      'class' => implode(' ', $classes),
     );
   }
 

src/view/phui/PHUIPropertyListView.php

@@ -284,7 +284,7 @@ final class PHUIPropertyListView extends AphrontView {
     return phutil_tag(
       'div',
       array(
-        'class' => implode($classes, ' '),
+        'class' => implode(' ', $classes),
       ),
       $part['content']);
   }
@@ -295,7 +295,7 @@ final class PHUIPropertyListView extends AphrontView {
     return phutil_tag(
       'div',
       array(
-        'class' => implode($classes, ' '),
+        'class' => implode(' ', $classes),
       ),
       $part['content']);
   }

src/view/phui/PHUITwoColumnView.php

@@ -220,7 +220,7 @@ final class PHUITwoColumnView extends AphrontTagView {
     return phutil_tag(
       'div',
       array(
-        'class' => implode($classes, ' '),
+        'class' => implode(' ', $classes),
       ),
       array(
         $navigation,