Use CTools' plugin system to declare resources.

Currently all resources are defined in a way a bit similar to CTools plugin, that try to include only the necessary files.

Since Services is already using CTools I think it will gain from adopting the plugin system as-well. Note that if you are going to do it, you should take an example from modules like CTools, Panels or Message that use the "new" plugin (i.e. not like context module, that is currently declaring the plugin in a hook instead of $plugin = ... ).