Added image-group-information-changed event

Author: wpferguson

content/lua.api.manual/events/image-group-information-changed.md

@@ -0,0 +1,32 @@
+---
+title: image-group-information-changed
+id: image-group-information-changed
+weight: 42
+draft: false
+author: "people"
+---
+
+`event`
+
+This event is called when image grouping information changes.
+
+# image-group-information-changed.callback
+
+```
+function(
+  event : string,
+  reason : string,
+  image : types.dt_lua_image_t,
+  group_leader : types.dt_lua_image_t
+)
+```
+
+* **event** - _string_ - The name of the event that triggered the callback.
+* **reason** - _string_ - The reason grouping changed.  One of add, remove, leader-change, remove-leader.
+* **image** - _[types.dt_lua_image_t](../types/dt_lua_image_t)_ - The image object that the change applies to.
+* **group_leader** - _[types.dt_lua_image_t](../types/dt_lua_image_t)_ - The image object that is the group leader
+
+# image-group-information-changed.extra registration parameters
+
+This event has no extra registration parameters.
+