Moved number classes/functions to storm/numbers

[volkm]

Somewhat related to #1033

New folder storm/numbers contains functionality for numbers:

• constants.h and ConstantsComparator.h
• KwekMehlhorn and RationalApproximation
• NumberTraits
• rationalfunction.h

Also use a new namespace storm::numbers instead of storm::utility.
This required a lot of replacements of e.g. storm::utility::one<..> to storm::numbers::one<..> but I think this gives a nicer structure in the future.

[tquatmann]

I like that this change, but I don't like that this will create a merge conflict in approximately every open pull request. Could we delay this a bit?

Also, I'll vote for storm::numbers::convert instead of storm::numbers::convertNumber.

[volkm]

Sure, we can definitely delay. Not sure whether we can find a timeframe with no open PRs, but I agree that too many open PRs are conflicting at the moment.

I like the idea of numbers::convert, will change it.