Support environment variables in papyrus project files

[Jampi0n]

Is your feature request related to a problem? Please describe.
The game path and therefore also the path of the game scripts is different from user to user. In order for the papyrus project to be portable, import paths should support different paths per user.

Describe the solution you'd like
Supporting environment variables in the papyrus project file would make the papyrus project more portable.

Describe alternatives you've considered
Do not publish the papyrus project with the mod, since it is not portable. Instead give instructions on how to create one, or provide a program, which generates the papyrus project file automatically.

Additional context
Example:
<Import>%Skyrim32Path%\Data\Scripts\Source</Import>