Add per-worker stats page with cumulative work and luck

Expose ckpool's per-worker cumulative shares via patch 0004, add a
WorkerDetailPage with hashrate, status, best share with per-worker luck
(bestever/shares*100), and total work with pool share percentage.
Worker names are now clickable in MinersTable and UserDetailPage.
Also centers numeric columns below their headers.

ui/src/app.css

@@ -140,7 +140,7 @@ tbody tr:hover {
 }
 td.num,
 th.num {
-  text-align: right;
+  text-align: center;
 }
 
 .badge {