* Fixed issue #94 where the user was prompted to select their Path of Exile data directory after every upgrade.
* The default Path of Exile data directory is now automatically chosen on first run if it exists
* Moved CommonOpenFileDialog usage to new DialogService class
* Changed Custom Sounds code in ItemFilterScriptViewModel to use ItemFilterScriptDirectory instead of DefaultPathOfExileDirectory
* Moved Custom Sounds code from constructor to Initialise method to prevent the files being enumerated before the directory is set during startup
