fix: missing backer information and cross origin errors

[brymut]

Resolves #1465

Description

Fixed a couple of errors:

• Empty backers list in issue/bounty page due to bounty_refunded failing query
• Cross-origin errors caused by failing API calls due to some routing errors and a querying error.

Changes made

• Change made in #1454 broke the bounty not_refunded query. Affecting the backer's list in the issue/bounty page, switched to OR.
• Removed .pluck method call as the switch to find_by in #1442 returns the model instance (instead of a collection like previously) which does not have the method. Refer to person_id field directly.
• Disabled 'autotrack' to stop Mixpanel client lib from calling decide API route.
• Changed 'track' API route for Mixpanel to accept appropriate POST method instead of GET which doesn't accept the send form data.

[brymut]

Hi @alphashuro, I think that should be it now. Could you please have another quick look?