Enhance credentials file loading logic

[Michele Pasin]

Logic
a) if dsl.ini credentials file in WD that overrides everything
b) try user level credentials ("~/.dimensions/")
c) try navigating up directory tree for dsl.ini

This way we xan support better the following scenarios
=> a) and c) are useful for jupyter notebooks without system wide installation
=> b) is the usual case for CLI

[Michele Pasin]

1ccfb6e