BUG/API: Fix operating with timedelta64/pd.offsets on rhs of a datelike series/index
closes #4532
closes #4134
closes #4135 
closes #4521

Timedeltas can be converted to other ‘frequencies’ by dividing by another timedelta.

```
In [210]: td = Series(date_range('20130101',periods=4))-Series(date_range('20121201',periods=4))

In [211]: td[2] += np.timedelta64(timedelta(minutes=5,seconds=3))

In [212]: td[3] = np.nan

In [213]: td

0   31 days, 00:00:00
1   31 days, 00:00:00
2   31 days, 00:05:03
3                 NaT
dtype: timedelta64[ns]
```

to days

```
In [214]: td / np.timedelta64(1,'D')

0    31.000000
1    31.000000
2    31.003507
3          NaN
dtype: float64
```

to seconds

```
In [215]: td / np.timedelta64(1,'s')

0    2678400
1    2678400
2    2678703
3        NaN
dtype: float64
```

Dividing or multiplying a timedelta64[ns] Series by an integer or integer Series yields a float64 dtyped Series.

```
In [216]: td * -1

0   -31 days, 00:00:00
1   -31 days, 00:00:00
2   -31 days, 00:05:03
3                  NaT
dtype: timedelta64[ns]

In [217]: td * Series([1,2,3,4])

0   31 days, 00:00:00
1   62 days, 00:00:00
2   93 days, 00:15:09
3                 NaT
dtype: timedelta64[ns]
```
