Major code updates - see description

-Windows 7 taskbar progress support
-Tidied up code with more classes
-Added multithreading for single pings
-Decreased ping timeout
-Added PingStatus enum with "Error" status for hosts that fail to be
resolved by DNS
-Fix next update time bug

TODO
-Multiple host selection support
-UI improvements
-Add comments and more code cleaning
-Multithreading for single selection refreshes