Add input-combo-icon for lock keys status
Added input-combo-icon for the purpose of displaying the status of multiple lock keys; i.e., Capslock + Numlock. There are no other icons that represent multiple lock keys. The keyboardindicator applet will utilize this new input-combo-icon upon the successful merge of commit 3748077b4f3e3d469e89664b5d7b12d4166f5543.
