This commit moves the presets subsystem to a location within the admin
folder, which is more appropriate given its purpose and reduces
developer frustration with tab completion of the admin directory.
A new component has been created, core_adminpresets, and tables and some
API methods from this tool have been moved there, so it can spread over
other plugins.
Currently, the tool_admin_presets plugin only provides the UI to interact
with the core adminpresets stuff.