Improve limit code to not depend on offline stuff

[lucalavezzo]

makeDataCard, runcards, init in particular, are very dependent on the offline analysis schema.
Should have some option for the analysis type, and move everything in functions or something to better handle different analyses?
Or are the scripts going to be changed so much that it's not worth it? In that case, should we rename them?

[lucalavezzo]

makeDataCard and runcard addressed in #39 . Need to look more into __init__ and runcombine, which still have some offline-dependent stuff.