#11 Remove copies of libraries

and use requirements.txt instead.

This includes corresponding updates in the example scripts and documentation.

This PR also includes the last change required by #5 (update xls sheets accordingly)

@denker This PR currently fixes the neo, elephant and odml version in the requirements.txt to the previously provided versions. In principle we could permit any version up to the current ones. Would you like to integrate this already in this PR or do you prefer a separate one?

Update: f4a1e30d78 extends the supported package versions and adjusts the codebase and example scripts accordingly. I also added an upper limit to the package versions matching the currently available versions that I tested.