css: Checkbox Vertical Alignment

This addresses a small issue where the system shows inline checkboxes
centered at the bottom of the text which makes it look out of place. This
updates the CSS for `input[type=checkbox]` to make the `vertical-align`
property equal to `middle` which renders the checkbox correctly.

scp/css/scp.css

@@ -3585,7 +3585,7 @@ input[type=checkbox] {
   padding: 0;
   margin:0;
   margin-right: 0.1em;
-  vertical-align: bottom;
+  vertical-align: middle;
   position: relative;
   top: -0.05em;
   *overflow: hidden;