Moves Clear to IIntervalCollection and adds AddAll method. Allows us to do generic contracts for Clear.
Adds boolean IsReadOnly property to IIntervalCollection. If true Add, AddAll, Remove, and Clear will throw a ReadOnlyCollectionException.
Quick fixes Count for old IBS tree to get tests to not fail. This is a valid implementation, but not very effective!
Adds more contracts to interval classes
Merge branch 'master' of https://github.com/lundmikkel/C5