[TYPO3-commerce] RFC 7738: basketStoragePid through setup

[Rik Willems]

Currently the pid where baskets are stored can only be set globaly 
through the EM. This patch adds a config variable that is read through 
the setup. This way you can use multiple shops/baskets on one installation.

To maintain backward compatability a check is made if the setting 
exists. If it doesn't the EM setting is taken.

Looking forward to your feedback!

Forge has a diff.txt to check it out: 
http://forge.typo3.org/issues/show/7738

Cheers, Rik