add temporal dimension to data structure (versioning)

[skasberger]

right now, only a snapshots of the actual website is possible, but it would be very interesting to store and compare the changes over time. for this the data structure needs to be versioned, which means it must add a temporal dimension. maybe to add a chronological ordered list between the sequential keys and the data from the organisations would be a way for this. additionally it would be necessary to write a download and diff script. also to think about possible interesting analysis and visualization over time would be helpful to find the proper data-structure and workflow.