remove unused ConstantTypeList, join FixedTypeList and TypeList, and fix them

[erickvermot]

ConstantTypeList is never used.
TypeList is only used by FixedTypeList, and already behaves as if the list had fixed type.

+ FixedTypeList needs many fixes, specially regarding elements sizes, since it considers that elements of the same type have the same size.

in the closed PR #392 I fixed many of them. Since the PR was rejected, I separated a few of those fixes here: https://github.com/erickvermot/python-openflow/tree/list_fix
Issue #415 will allow more fixes from the PR.