Add ReplaceableTable interface

[senderista]

For classes like MutableTupleBuffer that allow random writes to cells, we have no interface comparable to ReadableTable or AppendableTable to represent the random write functionality. Just like we have ReplaceableColumn, we need ReplaceableTable for random write semantics.

[jingjingwang]

Furthermore, I think some of our existing interfaces are designed with funny method names: WritableColumn has a bunch of append(), but AppendableTable has a bunch of put(). Readable is probably redundant since we don't really have Unreadable. And we can't cast Column<?> to be ReadableColumn.

[senderista]

I think ReadableTable/ReadableColumn still makes sense for impls that only implement that interface. How else would they say "I'm a read-only table/column"?

I think maybe we should do away with the generic Column<> type altogether. I've literally never been able to parametrize it with a type and had the code compile--it's just Column<?> everywhere, which is pointless.

Agreed that put() doesn't sufficiently convey the idea of "append", and it would be better to just have methods called append() on AppendableTable.