AddressMask: A distinct type for bitmasking addresses

[dahlia]

Continued from the patch #197.

Problems:

• Several interfaces store a bitmask of addresses into Address type. This leads to misunderstand these values are a valid address, which is not true.
• Although the WildcardMask constant is defined, but it is placed in an inappropriate place: BlockSet<T>. It should be treated like AddressMask.Wildcard instead.
• Matching algorithm is also placed in a random place. It should be abstracted out like IsPossiblyIn(this Address, AddressMask) or IsDefinitelyNotIn(this Address, AddressMask).
• Adding an Address into a bitmask is also placed in a random place. It should be abstracted out like AddressMask.Add(Address).

[dahlia]

It is no more valid because we don't use address masking since #232.