Preparation for Support .NET 4 or 4.5

* All: Added the dependency with metadata.h.
* All: Deleted all CoInitialize/CoUninitialize call because they are unnecessary on the api of .NET 4 or 4.5.
* All: Publish method Initialize, because it has the intent that is same as the constructor.
* Hosting: Associate HostInfo, it is the entry point to the hosting api, with ICLRMetaHost.
* Hosting: Associate RuntimeHost, it expresses the .NET Runtime, with ICLRRuntimeInfo.
* Metadata: Change the source that gets IMetaDataDispenserEx to ICLRRuntimeInfo.
* StrongNaming: Replace free functions to the members of ICLRStrongName.