Add 7zip support

[Roemer]

Would be great to have 7zip support (dependent on a nuget package like 7-Zip.x64 for command line or SevenZipSharp) to allow compressing with 7zip.
Background is that the .net < 4.6.1 ZipCompress does remove empty folders. Also having .7z support would be great ;)

[akordowski]

Thank you for the suggestion. I will take a look into it.