Solved Problem 9

implemented a fibonacci Sequencer class (I thought I would need it for problem 9, turns out I don't)
add Combinatorics class (thought I would need it for problem 9, turns out I don't)
update PrimeNumbers class to use a static constructor instead of a manual one.
had to update several projects that used PrimeNumbers class, and remove the called to the old initializer.
using ulong instead of UInt64 (easier to type) in prime numbers