make the max height of the swimlane not too big

We should take a full screen minus the header height

client/components/swimlanes/swimlanes.styl

@@ -7,7 +7,7 @@
   display: flex
   flex-direction: row
   overflow: 0;
-  max-height: 100%
+  max-height: calc(100% - 26px)
 
   &.placeholder
     background-color: rgba(0, 0, 0, .2)