Create an in-memory-mock implementation for PDQ and XDS for integration testing

[bmehner]

For integration testing we need a lightweight implementation of PDQ and XDS interfaces. This implementation should be started by the build during the pre-integration-test phase and shutdown in the post-integration-test phase of maven.

Requirements are:

• PDQ should return a small list of patients regardless of the parameters supplied for the query.
• There is only one in memory store of consents regardless which patient id is given as parameter.
• Other document types than Consent Documents are rejected.
• Fast startup and teardown as it will be executed during the build.

Prerequisite for issue #8

[bmehner]

A new section called "mocks" has been created. One or more modules will be implemented here in order to provide the required in memory implementation.