(API Change) libobs: Don't use signal for obs_load_sources

(Note: This commit also changes the UI)

Changed:
-------------------
void obs_load_sources(obs_data_array_t *sources_list);

To:
-------------------
void obs_load_sources(obs_data_array_t *sources_list,
		obs_source_load_cb callback, void *private_data);

Signals should really never be required to use to make some function
work properly.  The "source_load" signal was required for the
obs_load_sources function, but it's meant more for loading private data
in the settings, not for general loading of sources.

This changes it so that a callback is explicitly required to load the
sources.

libobs/obs.h

@@ -550,8 +550,11 @@ EXPORT obs_data_t *obs_save_source(obs_source_t *source);
 /** Loads a source from settings data */
 EXPORT obs_source_t *obs_load_source(obs_data_t *data);
 
+typedef void (*obs_load_source_cb)(void *private_data, obs_source_t *source);
+
 /** Loads sources from a data array */
-EXPORT void obs_load_sources(obs_data_array_t *array);
+EXPORT void obs_load_sources(obs_data_array_t *array, obs_load_source_cb cb,
+		void *private_data);
 
 /** Saves sources to a data array */
 EXPORT obs_data_array_t *obs_save_sources(void);