MDL-46282 core: Add VERP API

This issue is a part of the MDL-47194 Task.
This issue is a part of the MDL-39707 Epic.
MDL-47195 core: Add PSR-0 Autoloader

This issue is a part of the MDL-47194 Task.
This issue is a part of the MDL-39707 Epic.
MDL-47195 libraries: Add horde IMAP from Horde 5.2.1

This issue is a part of the MDL-47194 Task.
This issue is a part of the MDL-39707 Epic.
MDL-46284 core: Add e-mail fetcher from IMAP

This issue is a part of the MDL-47194 Task.
This issue is a part of the MDL-39707 Epic.