Added new APIs: list user-installed plugins and uninstall plugin.

Moved install and list plugin APIs to PluginController and updated their
service paths under /plugins.

Change-Id: I592408665672d52e2479671b97de5ba49e9a9c5a
diff --git a/core/Changes b/core/Changes
index 6a157f5..87d954c 100644
--- a/core/Changes
+++ b/core/Changes
@@ -1,6 +1,6 @@
 # version 0.68
 
- - Added OAuth2 scope: INSTALL_USER_CLIENT
+ - Added OAuth2 scopes: INSTALL_USER_CLIENT, UNINSTALL_USER_CLIENT
  - Added status codes