axes.js, vidjil.less : add "locus".pretty, and adapt css

See #2395

browser/css/vidjil.less

@@ -577,7 +577,7 @@ line {
   float: right;
   overflow: hidden;
   display: inline-block;
-  height: 16px;
+  max-height: 16px;
   position: relative;
 }
 

browser/js/axes.js

@@ -106,6 +106,10 @@ Axes.prototype = {
                 label: "locus",
                 axis: new GenericAxis(),
                 fct: function(clone){return clone.germline},
+                pretty: function(system){
+                    var ret = self.m.systemBox(system);
+                    return (ret instanceof Element ? ret.outerHTML : ret);
+                }
             },
             "Size" : {
                 doc: "ratio of the number of reads of each clone to the total number of reads in the selected locus",