libobs: Add services API, reduce repeated code

Add API for streaming services.  The services API simplifies the
creation of custom service features and user interface.

Custom streaming services later on will be able to do things such as:

 - Be able to use service-specific APIs via modules, allowing a more
   direct means of communicating with the service and requesting or
   setting service-specific information

 - Get URL/stream key via other means of authentication such as OAuth,
   or be able to build custom URLs for services that require that sort
   of thing.

 - Query information (such as viewer count, chat, follower
   notifications, and other information)

 - Set channel information (such as current game, current channel title,
   activating commercials)

Also, I reduce some repeated code that was used for all libobs objects.
This includes the name of the object, the private data, settings, as
well as the signal and procedure handlers.

I also switched to using linked lists for the global object lists,
rather than using an array of pointers (you could say it was..
pointless.)  ..Anyway, the linked list info is also stored in the shared
context data structure.