Implement Series.swapaxes

[xinrong-meng]

        >>> kser = ks.Series([1, 2, 3], index=["x", "y", "z"])
        >>> kser
        x    1
        y    2
        z    3
        dtype: int64
        >>>
        >>> kser.swapaxes(0, 0)
        x    1
        y    2
        z    3
        dtype: int64

ref #1929

[ueshin]

LGTM.

[itholic]

LGTM

[xinrong-meng]

Thank you @ueshin @itholic!

[codecov-io]

Codecov Report

Merging #1954 (f567157) into master (7e06e43) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1954      +/-   ##
==========================================
- Coverage   94.64%   94.63%   -0.02%     
==========================================
  Files          49       49              
  Lines       10828    10840      +12     
==========================================
+ Hits        10248    10258      +10     
- Misses        580      582       +2     

Impacted Files	Coverage Δ
databricks/koalas/frame.py	96.72% <ø> (-0.04%)	⬇️
databricks/koalas/missing/series.py	100.00% <ø> (ø)
databricks/koalas/series.py	96.88% <100.00%> (-0.09%)	⬇️
databricks/koalas/namespace.py	84.19% <0.00%> (-0.04%)	⬇️
databricks/koalas/missing/frame.py	100.00% <0.00%> (ø)
databricks/koalas/indexes.py	96.97% <0.00%> (+<0.01%)	⬆️
databricks/koalas/internal.py	96.49% <0.00%> (+0.02%)	⬆️

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