cally: Clean up the headers

cally: Clean up the headers

Make Cally follow the single-include header file policy of Clutter and
Cogl; this means making cally.h the single include header, and requires
a new cally-main.h file for the functions defined by cally.h.

Also:

  • clean up the licensing notice and remove the FSF address;

  • document the object structures (instance and class);

  • G_GNUC_CONST-ify the get_type() functions;

  • reduce the padding for CallyActor sub-classes;

  • reduce the amount of headers included.