Allow users to start/stop services in sudo mode

[asmiller]

Found your tool, and ran into the same issue as #7 . Here's a quick fix -

• Updated to Swift 5
• If a service was started by root, clicking it will stop it as root
• To toggle (start or stop) a service as root, hold down the Control key

[stefansundin]

@andrewn I think this change and #30 together would be great to merge and release a new version. I have recently started using dnscrypt-proxy which runs as root and needs to be restarted every time its config is updated, which can be a bit tedious.

If @asmiller is too busy to rebase this PR then I am volunteering to do it and open a new PR.

Thanks!