Support for external variables in .conf files

[iliassoto]

As of now, variables within the .conf files that reference externally defined resources are not parsed correctly. The same goes for variables that are given as parameters in the command line. For the SDLB, these variables primarily refer to environment variables.

A possible solution would be to define a second folder "envConfig" with a .conf file per environment that is to be included in the parsing step depending on the chosen environment. The environment itself can be defined in the manifest.json and passed to the main application.