FLUID-5247: Fix for incorrect treatment of escaped paths in Model Transformations with respect to schema

Incorporates modified test case for FLUID-5248 which is invalid as posted on the JIRA - see the discussion there. 
http://issues.fluidproject.org/browse/FLUID-5248

The fix for FLUID-5247 was best met by some wholesale cut and paste of upcoming material from the FLUID-3674 branch since the "accessor config" system was improved there to support this kind of use case. This has no real issues for the FLUID-3674 branch since all conflicts that this introduces in DataBinding.js will be discarded in any case.

@jobara, @kaspermarkus