BUG: inconsistency in division for scalar Offset vs series/array of Offsets
When dividing a scalar Offset with a numeric series, we get a timedelta64 series. But when dividing a Series of Offsets, we preserve the offsets.

```
In [26]: td = pd.offsets.Day(3)

In [27]: td / pd.Series([1, 2])
Out[27]: 
0   3 days 00:00:00
1   1 days 12:00:00
dtype: timedelta64[ns]

In [28]: pd.Series([td, td]) / pd.Series([1, 2])
Out[28]: 
0      <3 * Days>
1    <36 * Hours>
dtype: object
```

Also "scalar / scalar" operation gives an Offset.  


cc @jbrockmendel 