v1.0.8

Fixed versions of references Orleans NuGet packages to match the current one.
Switched message header keys from strings to enums for performance.
Fixed a deadlock issue in deactivation process.
Added a NuGet package to simplify testing of grain projects - Microsoft.Orleans.TestingHost.
Fixed regression of reporting codegen error to Visual Studio Errors window.
Added version to SDK msi product and folder name.
Other fixes and improvements.