Write buffer

[Avsecz]

-[/] Enable write buffer

• removed df_to_np_dict
• [x] run the file writing in background - implemented in https://github.com/kipoi/kipoi/pull/415

[coveralls]

Pull Request Test Coverage Report for Build 210

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.008%) to 76.384%

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Totals
Change from base Build 199:	-0.008%
Covered Lines:	2222
Relevant Lines:	2909

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💛 - Coveralls