peppol-lookup: DummyLookupClient implementation

[dladlk]

Discussed in #48

Implementation of the suggested change is developed in this issue.

[dladlk]

See branch with changes here: https://github.com/OxalisCommunity/vefa-peppol/tree/49-peppol-lookup-dummylookupclient-implementation

and pull request: #50