Extend a membership by completing a contribution

[jaapjansma]

I want to extend the membership period as soon as a pending contribution is set to completed.

The use case is:
I have a membership organisation and I collect membership payment with Sepa Direct Debit. When I create the file the contributions are automaticly linked to the membership (see #10). The contributions are immediatly set to completed as we deal with failures manually. Now I want that the membership is extended with the status current as sson as the contribution is set to completed.

Solution:
Provide a checkbox to enable/disable this functionality from the configuration and then whenever a contribution is updated and the status is set to completed we should extend the membership.

[jaapjansma]

I have implemented this below a screenshot of the setting screen

[bjendres]

@jaapjansma: Sounds/looks great. I'll have a look and merge when I'm back from BRX.

[jaapjansma]

@systopia I am going to add another commit to check whether the contribution is completed before extending the membership.

[jaapjansma]

I have updated the PR (#19). It now triggers when a contribution is completed. It will then check if the contribution is linked with a membership and if so (and the setting is enabled) then it will extend the membership end date.

[bjendres]

released with 0.5.1