CYB-352 Return DB connections to the pool after done with using raw SQL

 * use a block yielding to the execution statement so that the connection is only used
   within said block
 * decrease sidekiq concurrency, so fewer connections are used at once.

https://jira.ets.berkeley.edu/jira/browse/CYB-352
CYB-350 Database reset Thor task

 * also improves the student factory to reduce the change of canvas_id collisions,
   and also ties the email address to the name.
Merge pull request #210 from coyote/sql_get_gallery_data

CYB-352 Return DB connections to the pool after done with using raw SQL
Merge pull request #212 from coyote/clean_db_thor_task

CYB-350 Database reset Thor task
CYB-358 Process Youtube URLs

 * return empty thumbnail_url when a submitted URL is not YT or Vimeo
 * pass site_tag and site_id as string, not symbol

https://jira.ets.berkeley.edu/jira/browse/CYB-358
Merge pull request #213 from coyote/process_yt_urls

CYB-358 Process Youtube URLs
CYB-360 Reduce logging for sidekiq in production

* Turned logging level in production to WARN in a new sidekiq_config initializer

https://jira.ets.berkeley.edu/jira/browse/CYB-360
Merge pull request #214 from coyote/reduce_sidekiq_logging

CYB-360 Reduce logging for sidekiq in production