Refactoring: moved some package helper functions to PackageUtils.cpp
Added appCopyTextToClipboard()
UI:
- Added UIPackageScanDialog, connected to button on UIPackageDialog
- Separated UIProgressDialog code to ProgressDialog.cpp

Core:
- Added FString::operator+=
- Made NumGameFiles and NumForeignFiles global ("extern"), added GNumPackageFiles
- ScanPackages() now can work with UIProgressDialog
- Fixed leak (FArchive) in ScanPackage()