First version of integrity module

For the moment the module only provides an action to call on a node for checking integrity of its site.

Warning : this module is not yet safe to use in a production or sensitive environment. Especially, the action can be called by anyone, without requiring authentication or special permission. In this case, the user will only be able to check nodes on which he has read permission

The module is for the moment more aimed toward development environment and non-regression testing