ui: prune & gc: disallow collapse and add bottom margin

the intra-panel margin is still the same (10 + 0 == 7 + 3) but one
can now see the bottom border.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

www/datastore/PruneAndGC.js

@@ -94,9 +94,8 @@ Ext.define('PBS.Datastore.PruneAndGC', {
 	multi: true,
     },
     defaults: {
-	collapsible: true,
-	animCollapse: false,
-	margin: '10 10 0 10',
+	collapsible: false,
+	margin: '7 10 3 10',
     },
     items: [
 	{