tools: use CSS to paint table rows with alternating colors in the status page

Change-Id: I04416437e2b18b452bde2f478084090f92003a85
diff --git a/tools/nfd-status-http-server-files/style.css b/tools/nfd-status-http-server-files/style.css
index 176da83..5d4b828 100644
--- a/tools/nfd-status-http-server-files/style.css
+++ b/tools/nfd-status-http-server-files/style.css
@@ -150,7 +150,6 @@
     min-width: 20px;
 }
 
-
 tr.center td
 {
     text-align: center;
@@ -173,7 +172,7 @@
     padding: 0;
 }
 
-.odd {
+table.alt-row-colors > tbody > tr:nth-of-type(even) {
     background-color: #eeeeee;
 }