Schema correction and Schema descriptions added

Issue Summary

Hello!

I've been running version 6.x-2.0-beta1, and the schema module has giving me some warnings regarding diaporama:

* diaporama.vid is type int but its default 0 is PHP type string
* diaporama.nid is type int but its default 0 is PHP type string
* diaporama.ratio is type int but its default 1 is PHP type string
* diaporama.image_node is type int but its default 0 is PHP type string
* diaporama.embedded is type int but its default 0 is PHP type string

I've corrected this by removing the ' ' around the default value.

Also noted it didn't had description fields, so I added thoes and tryed to find a fitting description to them, although GoZ should take a look, I might not have understand the purpose of some of the tables. Changed the code format for better readability.

Here's a patch against version 6.x-2.0-beta1 with the changes for review. This should also be marked to be ported, after commiting to the 2.0 release.

Thanks GoZ for a great module!