Handle genome build information

[smlmbrt]

Mainly to stop combine_scorefiles from assuming all files are in the same build.

• Does explicit checking first to check if the scorefile is HmPOS and in the correct genome build, and uses those data
• If not, checks whether the current build == target_build and that it has chr_name/positions
  • Will fail if --liftover isn't selected and current_build != target_build
• Runs liftover

[smlmbrt]

Test fails because the sample file only has genome_build but I've renamed the chain_genome_build and chain_target_build to reflect that those are the build IDs in the hg notation that's needed to get the right chains.