ledger: update checkout/views.py

[wilsonc86]

fix up the "skip payment if free or if proxy applicant" functionality using local functions when get is called on PaymentDetailsView

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 627

• 7 of 8 (87.5%) changed or added relevant lines in 1 file are covered.
• 294 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.02%) to 35.959%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ledger/checkout/session.py	7	8	87.5%

Files with Coverage Reduction	New Missed Lines	%
mooring/pdf.py	1	0.0%
ledger/payments/bpay/crn.py	1	55.22%
mooring/models.py	3	0.0%
ledger/payments/models.py	3	91.25%
ledger/checkout/utils.py	27	70.64%
parkstay/api.py	76	18.29%
ledger/payments/utils.py	82	13.01%
parkstay/models.py	101	54.38%

Totals
Change from base Build 606:	0.02%
Covered Lines:	11487
Relevant Lines:	31945

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💛 - Coveralls

[scottp-dpaw]

Reviewed 2 of 2 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved