Replace TypeSet with Type Specifications

These are capable of representing infinite sets of types,
provide better clarity and simplicity in the type checking,
and resolves a number of inconsistencies that could occur.
Add coercion of Cypher Types
Correct type checking of functions
Remove CTLong

CTInteger is used consistently internally
Use covariant/invariant/contravariant specifiers instead of TypeSpec operators
Merge pull request #1786 from cleishm/cypher-types

Corrections and improvements to Cypher type system
Fixed property loading tx state leakage

when loading properties from a node or relationship the transaction state
was considered. This is not allowed since the result of such loading goes
into the cache. Fixed by disregarding transaction state there.
Merge pull request #1833 from tinwelint/2.0-no-cache-prop-load-issue

Fixed property loading tx state leakage