Review and consolidate migrated registration code

[govert]

To support improved 'extended registration' by default, we've duplicated much of the code from ExcelDna.Registration into ExcelDna.Integration. We would like to remove and deprecate ExcelDna.Registration.

• Currently helper methods in the registration pipeline like ProcessParamsRegistrations are marked internal. This means an add-in cannot define an 'explicit registration' approach which uses these helpers.
• We should make those methods that match the public interface of ExcelDna.Registration also public from ExcelDna.Integration, and in the same namespace as before.
• This should mean we can recompile examples like https://github.com/Excel-DNA/Samples/tree/master/Registration.Sample by just removing the ExcelDna.Registration package.

Finally, we should remove the code from ExcelDna.Registration and mark the package as Deprecated.

[govert]

One option would be to make a new set of public types inside ExcelDna.Integration that has the same namespace and names as the types in ExcelDna.Registration, but forwards the work to the types in ExtendedRegistration.
Another option is to rename and make public the corresponding types, to make them compatible with code that would have used ExcelDna.Registration before.

I think we should be able to move everything from ExcelDna.Registration and ExcelDna.Registration.VisualBasic into the main ExcelDna.Integration library.

For ExcelDna.Registration.FSharp, we should make and example with whatever the smallest snippet of code is that a user can add to their project to support the FSharp async type. We can put this inside the Registration.FSharp sample in the Samples repository. Maybe just this code as is: https://github.com/Excel-DNA/Registration/blob/master/Source/ExcelDna.Registration.FSharp/FsAsyncUtil.fs

The end result should we:

• Code that used ExcelDna.Registration.* should now compile and work without a package reference to ExcelDna.Registration. (With the exception of the F# addition, where an extra piece of code is needed in the user project).
• We deprecate the ExcelDna.Registration packages.
• Fix the Registration.* samples in the Samples repo (once we have the pre-release packages with the above changes).