support for "switching" default host/profile for managed domain

[Ladicek]

Currently, when creating Online|OfflineOptions for managed domain, one can specify a default host and/or default profile. This choice is then set in stone, which forces users to either completely avoid the convenience of transforming standalone operations to domain, or to create separate clients for each host/profile. Both options are unfriendly, the second additionally causes more overhead.

The API could be reworked a bit to address the issue. The default host/profile wouldn't be set in the Online|OfflineOptions. Instead, one would be able to create a host- and/or profile-specific Online|OfflineManagementClient from the "default" one by calling .forProfile or .forHost. These specific clients would delegate to the original management client and only perform the transformation.

If possible, this should be backwards-compatible. That's hard, though, because the default host and profile is currently publicly accessible from Online|OfflineOptions.

Thanks to @akostadinov for the basic idea of using a wrapper!