API method to get data from the declaration that corresponds to a contribution

As part of #16 (closed), I wrote an API method: getcontributioneligibility that facilitates reading fields from the declaration that corresponds to a contribution. There is already a merge request associated: !17 (merged).

Usage Example

The main use case of the new API method is to be able to add information from the Gift Aid declaration that corresponds to a contribution, when designing a receipt template. The goal is to write templates that can be used to both print receipts for new contributions or reprint them for old ones.

{crmAPI var='contribution_giftaid_declaration' entity='GiftAid' action='getcontributioneligibility'
    sequential=0 contribution_id=$contributionID}

{crmAPI var='contribution_eligible' entity='OptionValue' action='get'
    sequential=1 return='label' value=$contribution_giftaid_declaration.values.eligible_for_gift_aid
    option_group_id='eligibility_declaration_options'}

{assign var='eligible' value=$contribution_eligible.values.0.label}

{if isset($eligible)}
    <tr>
        <td {$labelStyle}>
            {ts}Eligible for Gift Aid?{/ts}
        </td>
        <td {$valueStyle}>
            {$eligible}
        </td>
    </tr>
{/if}