Add multiple virtual environments functionality

Parts of the code used in MONAPipe relies on package versions that are either outdated or incompatible with other parts of the code. We need a functionaility that makes it possible to execute parts of MONAPipe's code in different virtual environments. Specifically, we need:

• A directory structure to manage the (additional) virtual environments, including the installed package versions / requirements.
• A directory structure to manage the corresponding "legacy" code (could be in the same directory structure), if it is not possible to leave the code in place and just switch the environment.
• An interface that installs, activates and transfers data to and from virtual enviroments.