AssemblyRequirement tracks own AssemblyCopyMode

* Remove Move(string, AssemblyCopyMode) now that AssemblyRequirement
  tracks its own copy mode when constructed.
* Add additional constructors to specify AssemblyCopyMode, the original
  two now default to the "Once" copy mode
* Add additional RequireAssemblyXYZ overloads to have an
  AssemblyCopyMode
* RequireAssemblyXYZ methods without AssemblyCopyMode defer to the
  AssemblyCopyMode on RemoteDomainExpression