Adding Bigtable RowFilter base class.

[dhermes]

Also adding regex filters for a row key (bytes) and a family name (string).

These come from

https://github.com/GoogleCloudPlatform/cloud-bigtable-client/blob/6a498cd3e660c7ed18299e980c1658d67661e69b/bigtable-protos/src/main/proto/google/bigtable/v1/bigtable_data.proto#L321-L404

In addition to more classes for primitive properties, parent classes are forthcoming to handle the non-primitive cases of filter Chain, Interleave and Condition (ternary).

Also renaming some redunant unit test names in test_column_family.py and ditching use of NotImplementedError in bigtable base classes (for both GC rule and row filter).

[dhermes]

@tseaver As with #1290 I am very open to breaking this class with 13 possible filters into 13 separate classes, but wanted to get the pattern in full view before we make a decision in #1290.

[dhermes]

@tseaver I'm going to start with just two here.

[dhermes]

@tseaver PTAL. I opted not to have regex filters inherit from a parent, but these ended up having also identical unit tests, so maybe it would've been worth it? I figured it was unnecessary since the classes to so little. (FWIW of the 19 filters, 4 of them are regex filters)

[tseaver]

If four of the filters take only a regex ctor argument, and differ only in terms of how they construct the protobuf, then factoring out __init__, __eq__, and __ne__ into a base class seems like a win.

[dhermes]

OK. Will re-factor. __ne__ is already in the main base class, but the other 2 are still uniform. Will ping once done.

[dhermes]

@tseaver PTAL. I added _RegexFilter as a base class.

[dhermes]

@tseaver PTAL I dropped all the virtual to_pb methods.

[tseaver]

LGTM