Add flags to highlight reports on pledge taker getting reported multiple times / Adds list of other reports on the same user in report review page

[wninohira]

Summary

This pull request addresses parts of #20, and allows moderator to see which reports are about a user that has gotten reported multiple times (= more urgent reports). Implementation is based on the moderation experience of the IDL lab group and the discussion among us. It has two main interface changes in report list view and report detail view.
*This is not ready to get merged into the live codebase until the rake task to look up twitch-id for all existing reports is ready.

Report list view

An icon to show that the user has been reported multiple times and the number is displayed next to their twitch username.

Report detail view

Added "other reports" section to show other reports about the same user. It looks up user based on the twitch id. It also shows the status of the reports (Unsolved / warned / dismissed / revoked )

Implementation note

• Adding twitch_id to report model
  • adds column twitch_id to report model
  • Updates report reception process so that twitch_id for the reported username gets looked up and added to data
  • TODO: make a rake task that looks up twitch_id for existing reports
• Adding association between report and pledge
  • Adds column reports_count to pledge model
  • makes a rake task that resets the initial value for reports_count based on the existing reports

Note for merging

1. Run migration
2. run twitch_id lookup rake task (not in this PR)
3. run reports_count resetter rake task