CSS: new 'spacer' class for div

In 1.2.x we used to add a table row with a 'spacer' class to separate
rows in a table.

This commit introduces a new class that can be used in form container
divs to separate field container divs:

Before:
	<table>
		<tr>...</tr>
		<tr class="spacer"></tr>
		<tr>...</tr>
	</table>
Now:
	<div class="form-container">
		<div class="field-container">...</div>
		<div class="field-container spacer">...</div>
	</div>

css/default.css

@@ -644,6 +644,7 @@ div.form-container .file  input,
 .display-value span {
 	max-width: 98%;
 }
+div.form-container .spacer { margin-top: .5em; clear: both; }
 .label-style {
 	position: absolute;
 	top: 0em;