[FEATURE] Complete target-based find modules and CMake-based pyopenms builds

[jpfeuffer]

Description

• Adds imported targets for all find modules that are not yet available as an official CMake module
• Use the targets to have transitive includes and lib dependencies
• Switch pyopenms to a CMake-based build (all the code in setup.py is just there for backwards compatibility)
• Add real export capabilities for people developing with OpenMS

With this, a completely separate pyopenms build could be achieved in the future, based on an installed OpeMS. We probably need to ship the PXDs, kind of like

[jpfeuffer]

Seems like we build contrib with non-standard names. We might need to re-introduce the find modules and maintain them.
EDIT: Seems like the contrib share was missing for Eigen. And some CMake configuration in the find_package call should be enough.

[jpfeuffer]

rebuild jenkins

[jpfeuffer]

rebuild jenkins

[jpfeuffer]

rebuild jenkins

[jpfeuffer]

/rebase

[timosachsenberg]

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[jpfeuffer]

Going to merge. Expect trouble in the next days.