add id to assigned_issue_ids no matter what

Since we're memoizing assigned_issue_ids we should be adding all issue ids to the array so they're not present on future queries.
Track last clicked issue

This is step 1 in a multi step process to increase the usefulness and decrease the annoying factor of codetriage. We can start by keeping track of which issues people actually click.

We'll expose this information in the subject line when a user hasn't clicked on an email in a few days.

Eventually we could use this information to send less emails. For instance if a user hasn't clicked on an email for the last 3 days, wait ~7 days before sending them another. We can always tweak this logic.

Either way the beginning point is tracking user clicks, and exposing that information

cc/ @olivierlacan
Merge pull request #256 from codetriage/schneems/click-track

Track last clicked issue
Fix links in daily e-mail

E-mails are rendered with the link to the issue pointing at
`issue_assignments/<number>/users/<number>/click` instead of the
complete URL.
Merge pull request #257 from leafac/fix-daily-mail-link

Fix links in daily e-mail
use assignment's repo
fix send_triage emails
fix send single email
fix the fixtures

We want to use implicit associations instead of hardcoded ids
Merge pull request #259 from codetriage/schneems/fuuuuuu-fixtures

fix the fixtures
handle false
rev git_hub_bub
fix find_each syntax
handle assignments that are blank
better time elapsed estimate
Refactor assignment logic into class

We're also decoupling the assigning and sending of issues. We're accomplishing this by adding a "delivered" flag on an assigned issue.
more efficient SQL query
cleanup
Throttle emails

If a user hasn't clicked on an email in the last 3 days, we drop them down to twice a week. If they haven't clicked in 14 days, we go to once a week.
fix tests