Support for ACL permissions per module in com_modules

This pull request allows to set permissions per module in the Joomla Module Manager. So besides configuring the com_modules general permissions you can configure the permissions per module. 

You can use this for example to: 
- allow access to com_modules, but only editing a selection of modules
- allow access to com_modules and edit all modules expect one (or more)
- disable state changes for certain modules
- etc..

## Notes
This patch doesn't include the SQL changes for all sample data sets yet. I am working on that but would suggest to review the code meanwhile.

## JoomlaCode Tracker Item
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=28638

## Testers welcome!
Testers are much welcome, let me know if you have any questions / feedback. Thanks in advance!