CMake Upgrade Steps

[sjunges]

Our Build & Configuration process had/has grown convoluted and unsuitable for many configurations.

We have been working towards better support. This issue tracks problems and provides an overview of TODOs.

• 1. Carl configuration at config-time workaround replaced by fetch_content, which is generally advised to use. This incentivized updates in the carl cmake.
• 2. Make sure the storm-starter-project can include storm via fetch-content.
• 3. Installation of executables/binaries such that afterwards, the build folder can be erased
• 4. Installation of developer-libraries, such that one can link new libraries to storm while storm is only installed.
• 5. Cmake config export for libraries that want to find storm targets
• 6. Allow stormpy to fetch storm and install
• 7. CPack support.
• 8. Generally, replace writing to various variables that are not to be written, such as CMAKE_CXX_FLAGS (which is important for including Storm via fetch content, see 2 and 6).
• 9. Do not use GLOB for source files, it is considered a bad practice.
• 10. Uniform installation paths for resources (this is a mess, see comment by @volkm in Cmake updates #602)
• 11. GTest is still added in a old-fashioned way, see below.
• 12. Autotools requires "old" timestamps which can break cmake builds when updating the storm version. This means that we need to be very careful when changing the spot version.

Current status.
1-5 are part of #602
For 6, this also requires some other changes to the build process.
For 7: Currently not working on.
For 8: I will not track these changes here right now.

[sjunges]

From @volkm:

As the way we include gtest is very old, we may want to update this soonishly

We could try to replace it with:

FetchContent_Declare(
googletest
URL https://github.com/google/googletest/archive/03597a01ee50ed33e9dfd640b249b4be3799d395.zip
)
FetchContent_MakeAvailable(googletest)