[DONT MERGE YET] Fixes/git crawl + v3 api

## Overview
Github imposes a max 1000 results limit on searches. To get around this we search by letter, giving us 1000 max results per letter. This is similar to the approach proposed by @kikko of searching by year, but gives more even distribution since the number of addons per year increase exponentially as it gets more popular. The alphabet method was suggested by Adam in a recent IRC meetup. 

This PR adds the following but still needs some help to be working 100 percent:

- [x] Add search by alphabet funionality
- [x] Up timeout to allow long running processes for testing locally
- [x] Fix missing base_url's in git class
- [ ] Fix different api return structure from v3

## To test 

The new auth method requires setting ENV variables, and this requires running the app with `foreman start`. However this means that running `rake cron` to test the cron job still fails to authorize. To get around this I found the easiest method to test was to replace these lines https://github.com/atduskgreg/ofxaddons.com/blob/master/github_api.rb#L7-L11 with the following: 

``
CREDENTIALS = {
    "client_id"     => xxx,
    "client_secret" => xxx
  }
``

This temporary hard code removes the reliance on ENV variables for testing. Then you can run `rake cron` to run the import.