Various generalizations (schema, scripting, object classes).

Experimental and not finished yet.
Small improvements.
Implemented partially-remote mode of operation.
Now both modes work: local and this new one.

Refactored schema operations - standard Exchange schema is now
bundled with the connector, but local extensions are allowed.

Refactored PowerShell operations - implementation is now much more
clean (Exchange aspects are factored out).
A couple of smaller fixes and improvements.
Minor improvements (and hacks) in error handling.
Removing duplicate values when updating EmailAddresses attribute.
Treating ProxyAddressAlreadyExists properly.
Correctly throwing UnknownUidException when modifying non-existing AD objects.
Merge branch 'generalized-scripting-experiment'

Conflicts:
	connectors/dotnet/ActiveDirectoryConnector/Messages.resx