Make threshold widening available in the interval domain as well

[michael-schwarz]

Since #379, we can extract all constants appearing in a program. We use this to provide a threshold widening for octagon in our apron analysis.
In the interest of generality, the Interval domain in base and the Box domains in our apron analysis should also have the option to enable this.

It is particularly interesting for globals, since we do no narrowing for them.