add app_destroy hook which allows addons to perform post delete actions

Zotlabs/Lib/Apps.php

@@ -623,6 +623,7 @@ class Apps {
 							intval(TERM_OBJ_APP),
 							intval($x[0]['id'])
 						);
+						call_hooks('app_destroy', $x[0]);
 					}
 					else {
 						$r = q("update app set app_deleted = 1 where app_id = '%s' and app_channel = %d",

doc/hook/app_destroy.bb

@@ -0,0 +1,4 @@
+[h2]app_destroy[/h2]
+
+Allows addons to perform some post delete actions.
+

doc/hooklist.bb

@@ -52,6 +52,9 @@ Hooks allow plugins/addons to "hook into" the code at many points and alter the
 [zrl=[baseurl]/help/hook/api_perm_is_allowed]api_perm_is_allowed[/zrl]
 	Called when perm_is_allowed() is executed from an API call.
 
+[zrl=[baseurl]/help/hook/app_destroy]app_destroy[/zrl]
+	Called when an app is deleted
+
 [zrl=[baseurl]/help/hook/app_installed_filter]app_installed_filter[/zrl]
 	Called when determining whether an app is installed