layers: Rename Layer/library/json files for consistency

Renamed layers from (for example) xxx_DrawState to xxx_draw_state
Renamed JSON files
Renamed libraries
Renamed object_track.* to object_tracker.*
Renamed apidump.h to api_dump.h
Renamed screen_shot layer to screenshot
Renamed APIDump layer settings file options to ApiDump
Bug fixes here and there from prior renames
diff --git a/layers/threading.h b/layers/threading.h
index 2d909b1..f3ceabc 100644
--- a/layers/threading.h
+++ b/layers/threading.h
@@ -47,8 +47,8 @@
 };
 
 static std::unordered_map<void*, layer_data *> layer_data_map;
-static device_table_map                        Threading_device_table_map;
-static instance_table_map                      Threading_instance_table_map;
+static device_table_map                        threading_device_table_map;
+static instance_table_map                      threading_instance_table_map;
 
 static inline debug_report_data *mdd(const void* object)
 {