Refactor FeatureTable and BatchTable

[elfprince13]

a) FeatureTable should not inherit from BatchTable, but both should probably share a base-class.
b) Terminology that is specific to client formats (e.g. "global" vs "instance-wise" vs "point-wise") should not be part of the generic class interface; however, we need to make sure it supports the sub-tables for extensions and extras.
c) There is no need for any mutation. Each *Table instance should be constructed from a single collection that represents the entire table, and handle encoding that collection into the separate JSON and binary buffer portions. The result should be treated as effectively immutable.