Remove app.config and unused references
Simplify and optimize RemDuplicate
Remove "please run in admin mode" label, it's not needed
Add checkbox (with tooltip) to set "local hosts file only" option

Changes won't be made to system's hosts if this checkbox is checked
Simplify async code (modified date requests and data download)

Label with "Available updates (X/N)" is now automatically updated
Add MessageBox with error description when something goes wrong