add modsPath config value

[Fusselwurm]

• can be relative or absolute
• defaults to path (i.e. arma path)

(#147 was weird. second attempt here.)

[Dahlgren]

This will break GM and VN selection when set to other than game folder

[Dahlgren]

Linux server does not support absolute mod paths or relative paths to folders which are not children

This limitation would not apply with #156

[Fusselwurm]

hmm ok