Modified attribute handling for products

- Reworked ER model (deleted one table, added another)
- Added slider and dropdown as attribute selectors
Updated product attributes handling

- Added defaults and units to attributes (ER model)
- Added JS to nicely display customizations
- Added "attribute_n=value" to "add to cart" link
Cleaned up header, added documentation

- Deleted breadcrumb (sorry fränzi :) )
- Added documentation to some functions
- Added a class to figure out ShoppingCart (needs discussion)
Updated Brainstorming, fixed footer and added checkout.php
adapted Registration form to same type as Order Form
updated translation txt's 
created regForm.txt