Fixes #3281 : escape automatically text in directive, and add a RAW cons...

...traint for when you don't want to escpe them. System variable are automatically raw

The escaping replace \ by \\ and " by \"

In a nutshell:
- systemVariable will behave the same (non escaped automatically)
- all variables by default are escaped
- a contraint "raw" is created, allowing to define variable that we don't want to be escaped automatically