Change isReplacedByResources to isReplacedBy, replacesResources with replaces

[dionmcm]

Originally reported by John Grimes (Bitbucket: j0hngr1mes, GitHub: Unknown)

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This is what the extension structure currently looks like:

Medication
|- isReplacedByResources
|  |- isReplacedBy
|  |- replacementType
|  |- replacementDate
|-...
|- replacesResources
|  |- replacesResource
|  |- replacementType
|  |- replacementDate
|-...

This should be done in the same way as subsidy, and re-jigged to look like this:

Medication
|- isReplacedBy (valueReference)
|  |- replacementType
|  |- replacementDate
|-...
|- replaces (valueReference)
|  |- replacementType
|  |- replacementDate
|-...

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• Bitbucket: https://bitbucket.org/dion_mcmurtrie/medserve/issue/19