Allow users to clear locally stored donation history

[cesonha]

Please Read, this is a WIP

This is my first open source contribution and this PR is still a work in progress, I hope you can help me understand how can I put the translation and if this class is easily testable, but I will take my time to see how can i write some automated tests for it.

What does this do?

This will add a new preference in the SettingsFragment that enables the user to delete the local donation history. All this done respecting the business rules defined in the Phabricator ticket. The new preference only shows if the donation history is not empty and after the user deletes it the preference hides.

Why is this needed?

Please refer to the Phabricator's link Background section
Phabricator:
https://phabricator.wikimedia.org/T380662

Screenshot

[cesonha]

Hi everyone, this is my first contribution and I have some doubts that I would be happy to get some clarification:

• I saw that the iOS and Android Settings screen have a different UI and the preferences are organized in different sections, how can I know that the way I did is approved by the UX/UI team?
• What should I do regarding the translation/localization, do I need to do it by myself?
• What about unit tests, I understand that some classes might be easier to test than others, is there a discussion for that? I want to add tests to my PR but some guidance would be nice!
• Do we need a summary for this preference?