Abstract _.pick and _.omit via pick wrapper

Use a function generator to create `_.pick` and `_.omit` as they're essentially [the same function](https://github.com/megawac/underscore/commit/f7d56a26971c69b9c58f8c9949e509f849b74b43#diff-0f36b362a0b81d6f4d4bfd8a7413c75dR899).

We can expect a major performance improvement from this changeset for all cases of `_.omit` with some perf hit on the properties as argument case for `_.pick`