prefs: add "2 minutes" and "5 minutes" as possible timeouts

On some JS-heavy page, 1 minute is sometimes too short. As the global
problem, JS is single-threaded and therefore heavy computation may block
the same thread that should execute the timeout function. We could use a
worker to fix that but this would defeat our ability to detect a page is
stuck.

res/values/arrays.xml

@@ -21,6 +21,8 @@
       <item>20 seconds</item>
       <item>30 seconds</item>
       <item>1 minute</item>
+      <item>2 minutes</item>
+      <item>5 minutes</item>
     </string-array>
 
     <string-array name="pref_ping_timeout_values">
@@ -30,6 +32,8 @@
       <item>20000</item>
       <item>30000</item>
       <item>60000</item>
+      <item>120000</item>
+      <item>300000</item>
     </string-array>
 
 </resources>