Clean up pipelines

I'm not actually sure if we want to go this way or not, but the main changes here are:

• break the downloads of CI test files into another job, which can happen in parallel with the rest of the code is compiling
• use the needs keyword in the run jobs to ensure that they only run after their upstream download or compile jobs
• move all the environment setup into the before_script block
• Add another CI test for FTAG5 double b-tagging