Prevent screwed up layout on long Content-Types

Some Content-Types (especially Vendor specific Content-Types)
can be rather long. This breaks the layout so prevent
rendering too wide select boxes by default.

src/main/less/specs.less

@@ -365,6 +365,10 @@
         border: 1px solid #aaa;
     }
 
+    .parameter-content-type select {
+        max-width:300px;
+    }
+
     h1 {
         color: black;
         font-size: 1.5em;