Move format modules into plugins

I'd like to remove the format modules - they are confusing. The modules page doesn't allow a nice way to organise these together to make it clear what they are.

The obvious choice is ctools plugins, but it might be overkill since it is unlikely people will supply their own formats without contributing them to this module. I have other issues with ctools, and I think doing custom plugins will be quicker and easier to maintain. They don't even have to be plugins, they can be hardcoded into the module. Perhaps continuing to allow the current method of adding formats via modules should still be maintained.

The main problem is that the modules are based around hooks, rather than callbacks. Some of this will be easy to convert to callbacks... some not so much.