PERF: quantile now operates per block boosting perf / fix quantile with nan
closes #11623
closes #13098
There is a slight API change in that the returned Series are now named by the quantile.

this PR

```
In [1]: df = DataFrame(np.random.randn(1000, 3), columns=list('ABC'))

In [2]: %timeit df.quantile([0.1, 0.5], axis=1)
1000 loops, best of 3: 830 µs per loop
```

0.18.1

```
In [3]: df.quantile([0.1, 0.5], axis=1)
In [1]: df = DataFrame(np.random.randn(1000, 3), columns=list('ABC'))

In [2]: %timeit df.quantile([0.1, 0.5], axis=1)
1 loop, best of 3: 317 ms per loop
```
