[HH] HTTP sharer plugin stubs.
[Azoth CH] It's perfectly OK for entry to not be a MUC.

Fix for 77996920064c8d417b249f63be248bdaab115091.
[Azoth] Moved impl of AzothCommon to a separate static lib.

For #1358.
[Azoth] Added DummyMsgManager for #1358.
[Azoth] Moved CreateCoreMessage to IProxyObject for #1358.
[Azoth] CoreMessage::Store() for #1358.
[Azoth] Remove dummy messages when needed for #1358.
[Azoth OTRoid] Use CoreMessage for dummy messages.

Closes #1358.