Adding payload option for delete requests

[plinnegan]

In some rare cases such as updating collections like dataElementGroups a payload is required with a delete api request. For example the DHIS2 2.29 dev manual in section 1.9.4.2 shows an example of bulk removal of data elements from a dataElementGroup.

I have made changes to allow json or data parameters for delete.

[coveralls]

Pull Request Test Coverage Report for Build 176

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage remained the same at 100.0%

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Files with Coverage Reduction	New Missed Lines	%
dhis2/api.py	2	100.0%

Totals
Change from base Build 171:	0.0%
Covered Lines:	343
Relevant Lines:	343

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💛 - Coveralls