Swifter

* Added warnings/errors for swifter methods which do not exist when using modin dataframes
* Updated Dask Dataframe dependencies to require a more recent version
* Updated examples/speed benchmark notebooks

* Broken release

* Fixed bug with string, axis=1 applies for pandas dataframes that prevented swifter from leveraging modin for parallelization when returning a series instead of a dataframe

* Remove pickle5 hard dependency

* Reduce resources consumed by swifter by only importing modin/ray when necessary.
* Added `swifter.register_modin()` function, which gives access to `modin.DataFrame.swifter.apply(...)`, but is only required if modin is imported after swifter. If you import modin before swifter, this is not necessary.

Two major enhancements are included in this release, both involving the use of modin in swifter. Special thanks to Devin Petersohn for the collaboration.

1. Enable compatibility with modin dataframes. Compatibility not only allows modin dataframes to work with `df.swifter.apply(...)`, but still attempts to vectorize the operation which can lead to a performance boost.

Example:
python

import modin.pandas as pd
df = pd.DataFrame(...)
df.swifter.apply(...)


2. Significantly speed up swifter axis=1 string applies by using Modin, resolving a long-standing issue for swifter.
* Use Modin for axis=1 string applies, unless allow_dask_on_strings(True) is set. If that flag is set, still use Dask.
* NOTE: this means that allow_dask_on_strings() is no longer required to work with text data using swifter.