Rails upgrade to 3.2

Notes
---------

There are a few tests removed:

* Audit trail cucumber test which is now covered by the functional test
* perform sets the transaction isolation level to SERIALIZABLE to ensure atomic update

DEPRECATION WARNINGS
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* You're trying to create an attribute `_destroy'. (when deleting via nested attributes)
* ActiveSupport::Memoizable is deprecated and will be removed in future releases,simply use Ruby memoization pattern instead. (from older carrierwave)

Trying to update carrierwave to a version without the deprecation breaks the current implementation of pdf thumb nailing.