Make kpm support two kinds of local package folders

- KpmPackageFolder: repo\{id}\{version}\{id}.{version}.nupkg
- NuGetPackageFolder handles two kinds of layout:
    (1)repo\{id}.{version}\{id}.{version}.nupkg
    (2)repo\{id}.{version}.nupkg
Make the KRE names represent the runtime itself instead of TFM
- Changed mono45 to Mono and removed bitness
- Renamed svr50 to CLR
- Renamed svrc50 to CoreCLR
- Changed x64 to amd64

#598
Renamed variables for clarity