Remove per user-system template-engine configuration

                     
|Q            |A    |
|---          |---  |
|Bug Fix?     |yes  |
|New Feature? |no   |
|BC Breaks?   |yes  |
|Deprecations?|no   |
|Tests Pass?  |yes  |
|Fixed Tickets|GH-49|
|License      |MIT  |
|Doc PR       |     |
                     
This removes per user-system template-engine configuration.
Which was already broken, so instead allow to configure the engine globally (delegated to the fos_user)

Providing per user-system template-engine would require to much work for to little benefit.