Refactor ordering comparators

[mezpusz]

This PR fixes some annoying things in OrderingComparator and subclasses:

• KBOComparator uses info from KBO::State to duplicate less effort and code.
• OrderingComparator is created but not called by Ordering anymore, this allows more flexibility.
• OrderingComparator has now a default implementation.
• LPOComparator has been simplified and now it is created lazily on the fly, as eager creation of the entire tree was a bottleneck in some cases. This is not justified for KBOComparator yet, so I did not bother doing it now.

[quickbeam123]

TPTP performance (-i 2000) seems OK:

Sort by UNS 7341 ['problemsSTD_master8465_lpo_i2000.pkl'] 7344 ['problemsSTD_marton8471_lpo_i2000.pkl'] 7510 ['problemsSTD_master8465_i2000.pkl'] 7514 ['problemsSTD_marton8471_i2000.pkl']

(Of course, 4 problems are typically less than the variance of the used lrs, but is seems good enough.)

[quickbeam123]

And here the dpc version of this:

Sort by UNS 7355 ['problemsSTD_master8465_lpo_dpc_i2000.pkl'] 7360 ['problemsSTD_marton8471_lpo_dpc_i2000.pkl'] 7509 ['problemsSTD_master8465_dpc_i2000.pkl'] 7511 ['problemsSTD_marton8471_dpc_i2000.pkl']