Add support for using the credentials of the workspace owner instead of using the credentials of the logged user

[aarranz]

Anonymous users don't have valid credentials for accessing the context broker. Allowing widgets and operators use the credentials of the owner instead of using the credentials of the logged user will be a good starting point for improving the usefulness of shared workspaces requiring access to the context broker.

This will become a great feature once WireCloud improves the shareability options.

[aarranz]

Implemented in version 3.0.4