WIP: Remove protected attributes and use instead strong parameters.

Protected attributes are a deprecated rails feature. In Rails 4 they are replaced by strong parameters in controllers.
Totally removed protected attributes from the app.

WIP: put strong parameters in all controllers.
Change in nomenclature: "subscriptions-data" is now called "data-import" in controllers, views etc.

This brings nomenclature in line with models; the relevant model is called DataImport.
Renamed the private method that implements strong parameters security in DataImportsController.

This brings this method in line with the change in nomenclature from commit 2e1b26effa721324a77873c38e4173bf8200e219.
Fix tests broken by commit 2e1b26effa721324a77873c38e4173bf8200e219
Fixed unit test.
Added strong parameters to EntriesController.

The format of the parameters has changed a bit for easier integration with this security feature.

BTW I don't like the least bit the syntax that has to be used to allow a param of type array to be accepted by the whitelist.
Added strong parameters security to FeedsController and FoldersController.

The structure of the JSON sent via AJAX to these controllers has been simplified a bit. Only really needed parameters are sent, instead of serializing the whole form to POST it. Also a hidden field in a form has been removed, its value can be included more easily in the AJAX POST with coffeescript code.