move player name cache from localStorage to sessionStorage

this gives a simple method of expiring entries. also, prevents localStorage from filling up with thousands of player names over time
(ideally something controllable with configurable age should be used, but this was a quick and simple change to try first)

code/boot.js

@@ -518,6 +518,7 @@ function boot() {
   window.setupTaphold();
   window.setupStyles();
   window.setupDialogs();
+  window.setupPlayerNameCache();
   window.setupMap();
   window.setupGeosearch();
   window.setupRedeem();