Merging is already useful, but I want to add prepend/append attributes that
allow an action to appear before/after an action or at the beginning/end of an
Action XML files are processed in order. Actions are appended/prepended to the
action-list as they are encountered. Weights specify a location in the merged
action-list, just as they do already. We will track the number of prepended
actions in each action-list and add this to the weight of any subsequent loaded
actions, which would preserve the current ordering semantics.