CSS/controls: fix margin

Problem was that as of CSS voodoo "padding" is not possible for our
"controls" section. Some control components therefore got margins,
but that's pretty ugly. This patch fixes this but pretends that all
components sitting directly below "controls" provide a root node.

public/css/icinga/layout-structure.less

@@ -159,6 +159,10 @@ html {
   -webkit-border-radius: 0.2em;
 }
 
+.container .controls > * {
+  margin-left: 1em;
+}
+
 .container .controls h1 {
   margin-left: 1em;
   margin-right: 1em;