Resolve "Creating a new device with type plugin just returns a normal device"

- This commit is a interim solution that allows to create new devices with the `--type plugin` flag. 
The orchestrator will only request capabilities of the provided device and build/return all the necessary files.
Therefore the api has been adjusted to allow to 'only' create gostructs and do not fire up a whole csbi.

- Additionaly the issue #176 has been addressed and the bug while creating multiple cSBIs has been fixed.
Appending to the `.Methods` string of the global `SouthboundStruct` was the
root cause for this bug. Creating a copy of `SouthboundStruct` and using
the copy in the process fixes this issue.

## Related Issue
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#175 , #176

Closes #175