GUAC-825: Add surface support to guac_common_cursor.
GUAC-825: Stub guac_common_display implementation.
GUAC-825: Implement guac_common_display alloc/free.
GUAC-825: Implement guac_common_display dup/flush.
GUAC-825: Wrap layers in struct. Handle free of layers/buffers when display is freed.
GUAC-825: Implement buffer/layer alloc and free.
GUAC-825: Migrate bitmap drawing to guac_common_display.
GUAC-825: Migrate pointer to cursor of guac_common_display.
GUAC-825: Properly handle disconnect.