Main changes of this PR

This PR adds support for CMake to build preCICE as a static library.
The main change is a custom preciceConfig.cmake, which is based on the auto-generated one.

Motivation and additional information

Building CMake as a static library and then using it via the preciceConfig.cmake was not properly supported.
The auto-generated config lists all header-only/interface libraries as link dependencies. This is required as they themself may depend on a static/shared library.
Thus, this required to find dependencies such as jsoncpp, prettyprint, Eigen, NumPy etc.

Related to #801, #677

Author's checklist

• I added a changelog file with this PR number in docs/changelog/ if there are noteworthy changes.
• I ran tools/formatting/check-format and everything is formatted correctly.
• I sticked to C++14 features.
• I sticked to CMake version 3.10.
• I squashed / am about to squash all commits that should be seen as one.

Reviewers' checklist

• Does the changelog entry make sense? Is it formatted correctly?
• Do you understand the code changes?
• (more questions/tasks)