Made the inner class public, because it caused a ClassNotFoundException as soon as I add another prefs page, which does not even use that class... yes, really weird; really Eclipse
Adds preferences and matching page for some network properties.

- the HTTP time out (with a new default of 50 secs)
- the shortest time when polling a Task (still at 2 secs)
- the longest time when polling a Task (still at 20 secs)
Merge pull request #8 from egonw/2-networkPrefs

Allow setting of custom network properties. Addressing bug #3487.