fixes #208, part of neo-project/neo#1866
Obsoletes #347

This PR introduces Neo.UInt160, Neo.UInt256 and Neo.Cryptography.ECC.ECPoint to the Neo.SmartContract.Framework assembly. Note, these type namespaces were explicitly chosen to match their corresponding types in Neo.dll. Over the next few weeks, I'll be introducing additional PRs to further unify types in Neo and Neo.SmartContract.Framework as part of neo-project/neo#1866.

Because these types in the two assemblies have the same fully qualified namespace, an assembly that needs to reference Neo and Neo.SmartContract.Framework needs to use a reference alias to disambiguate. I've added appropriate reference aliases in Neo.Compiler.MSIL and the relevant unit tests projects.

Under the hood, these types are simple byte arrays, like how strings are handled in Neo smart contracts. These types are merely there to provide a small amount of compile time type safety + familiarity to the developer. Relevant service methods (such as Runtime.CheckWitness) and domain properties (such as Block.Hash) have been updated where appropriate to be strongly typed as UInt160, UInt256 or ECPoint.

Assorted Notes:

• SmartContract Framework types that wrap native contracts (such as NEO and Oracle) have been updated to expose their script hash as a static Hash property. To avoid declaring the script hash twice, NEON has been updated to look for a new NativeContractHashAttribute as a marker for the appropriate method to return the contract script hash.
• ConvertNewObj in NEON has been updated to support the default and byte array constructors of UInt160 and UInt256. Default constructor pushes a byte array of appropriate size onto to stack. Byte array constructors inject VM code to validate the byte array on the evaluation stack is of the expected size
• ECPoint in SmartContract.Framework has neither default or byte array constructors. I wasn't sure if these types were ever constructed from byte arrays in contracts. It would be straightforward to include these constructors similar to UInt160/UInt256's constructors.
• UInt160/UInt256 each have a static Zero property that pushes a zero array of appropriate length onto the stack via OpCodeAttribute
• FuncExport.ConvType recognizes the new types and returns the appropriate ContractParameterType value as a string
• ModuleConverter.IsContractCall was updated to return contract hash out parameter as UInt160 instead of a byte array