should we use `*.page` files to get keys?

[dneise]

At the moment the keys we use are hardcoded, e.g. here:
https://github.com/fact-project/smart_fact_crawler/blob/master/smart_fact_crawler/__init__.py#L68

But we could use the *.page files to get the keys e.g. this one:
http://fact-project.org/smartfact/struct/tracking.page

However the keys are not valid variable names. And in case there are multiple values in one line, as e.g. in
http://fact-project.org/smartfact/struct/fact.page
there is no valid variable name.

[maxnoe]

Maybe a better plan is not to use them as keys but to store the ones which were used to implement the current version and compare them to the ones on the server. Raising at least a warning if they do not match.