Fix file input styling

The file input on the bulk upload page looked a bit weird because
it was inheriting the .form-control styling meant for text inputs.
Now it doesn’t. Also, line-height:1em fixes a visual bug on Mac.

static/sass/_accounts.scss

@@ -1,11 +1,17 @@
 .account-form__field {
     margin-bottom: 1em;
 
-    input {
+    input[type="text"],
+    input[type="email"],
+    input[type="password"] {
         @extend .form-control;
     }
 }
 
+input[type="file"] {
+    line-height: 1em;
+}
+
 .account-form__field--error {
     color: $color_error_red;