Dynamic permissions

A new big feature of WityCMS will be the ability to filter actions depending on any table of any application.

The developer has to define a table that will be used to filter (categories for news) and automagically the end-user will be able to use these categories to set permission (for example a user will be able to edit one category but not another).

Two step of filtering: 
* When accessing the application to avoid unallowed access to an action with a given category
* When sending the model (to the view or directly to the user) to remove unallowed output content

**TODO:** 
* [ ] Choose the manifest syntax to describe where is the data source in the database and where to filter it in the model
* [ ] Choose the manifest syntax to describe the filtering policy (input and/or output datas filtering and/or disallowing access)
* [ ] Choose the database storing syntax
* [ ] Implement the getter in WSession
* [ ] Implement the manifest parsing
* [ ] Implement the input filtering (similar to ```hasAccess()```)
* [ ] Implement the output filtering
* [ ] Implement the GUI in the User application to easily edit these permissions

*The first commit of this branch show where these implementations could be done and give some possible ways to do it.*

Related to #31