Make tests and examples self-contained

[tkoskela]

A number of fixes to make tests, examples and benchmarks build and run without access to the source directories. We need this when building with Spack because the source won't be accessible after the build has completed. Everything the executables need should be installed in the install directory. I think this makes sense anyways, it's strange that the installed application has hidden dependencies on the source dir.

• Dependencies moved from CMakeLists.txt to dependencies.cmake for clarity
• Tests, Examples and Benchmarks are built explicitly with a relative path so that ctest finds them after they've been copied to the install directory
• Updated CMakeLists.txt of benchmarks to work with latest Google Benchmark
• Tests read data from install directory instead of source dir because that is guaranteed to be available

[20DM]

Is this one still WIP? 🤔

[tkoskela]

Nope, it's ready to go