Create REST API to provide data to KnockoutJS Frontend

[kuhnchris]

Create a restful API (for example via Flask) to provide data to the frontend.

1. Get list of bounties and their checkin status: /api/v1/checkin/bounties
2. Mark a bounty as reviewed: /api/v1/checkin/bounties POST request, body: `{'bounty_url':'', 'comments': '....'}` (edited) 
1 will return:

```[
{
'bounty_url': '...',
'funded_by': '....',
'status': '....',
'github_url': '',
'date_last_reviewed': None|<date>
}
.....
]```
(edited)