Refactor CMake

[CasparJungbacker]

Clean up and refactor our CMake infrastructure, using ECMWF's ecbuild helper functions.

• Use CMake presets for toolchain selection. Instead of using the SYST environment variable, a toolchain can be selected by providing --preset=<name> to the cmake command. For example:

cmake --preset=gnu ..

is equal to the old workflow of setting SYST=gnu-fast before calling cmake. To get a list of all defined presets, execute:

cmake --list-presets

• Renamed some compilation options. I will provide an updated list of these in the documentation.
• Renamed the DALES executable from dalesX.Y to just dales. The DALES library has been renamed to libdales.
• Disabled compilation of the DALES library by default.
• Update minimum CMake version to 3.17.
• Updated CI.