Fixed interface in dossiers ConstrainTypeDecider.

The default adapter should use `Interface` as adapting interface
for the request. Otherwise overriding the ConstrainTypeDecider
in a customer package, is not possible without inheriting from
`Products.CMFDefault.interfaces.ICMFDefaultSkin` in the customers browserlayer.
Merge pull request #259 from 4teamwork/pg_fix_constrainttype_decider

Fixed interface in dossiers ConstrainTypeDecider.
Added repository import directly from xls.
Moved examplecontent from csv to xls.
Added xls import tests.
Removed unnecessary pipeline definitions in xls import.
Added force-text macro in text form.