Alternative default config

[FreHu]

When a config file cannot be located, it will use the default one which is probably not what you want at all. I would like to have an option to use my own default, either by specifying the config in my user settings or a path to a custom abaplint.json.

[larshp]

issue moved to vscode-abaplint, as this is relevant in the context of an editor?

[larshp]

also see #35