Fix EZP-20684: Unable to update user object

This PR fixes issue https://jira.ez.no/browse/EZP-20684

The issue was in SPI Content cache not being cleared on updating User data, hence old cached Content being returned on loading User.

Additional:

* setting CSRF token intention to Legacy Stack when session based auth is used REST
* fixing input validation in ```UserService::updateUser()```
* moving reloading of User in ```UserService::updateUser()``` to the top for earlier possible throw
* when ContentInfo cache is cleared also clearing SPI Content cache - Content aggregates ContentInfo but is loaded independently