Fix the Redmine Impersonate plugin display

Add icon on button and improve message display

src/sass/components/_plugins.scss

@@ -52,6 +52,23 @@
 }
 
 
+//
+// Redmine Impersonate
+// https://www.redmine.org/plugins/redmine_impersonate
+// --------------------------------------------------
+
+#impersonate::before {
+  content: "\f21b";
+  display: inline-block;
+  margin-right: 5px;
+  font: normal normal normal 14px/1 FontAwesome;
+}
+
+#impersonation-bar {
+  border-radius: 0;
+}
+
+
 //
 // Redmine Backlogs
 // https://github.com/HolonGlobe/redmine_backlogs