CYB-321 Use Canvas' thumbnailing for non-YT/Vimeo URLs

* Adds a new model, GenericUrl
* Adds queries for #index and #show actions of the GalleryController

https://jira.ets.berkeley.edu/jira/browse/CYB-321
CYB-321 - Provide UI support for generic URL submission
CYB-321 - Added default thumbnail for submissions without a thumbnail image
CYB-321 - Removed transparent border around the default thumbnail
CYB-332 CSV taking nearly 4.5 minutes to generate

  * altered to get all data directly via SQL
  * no use of the Decorator anymore -- pure SQL + Ruby
Merge pull request #224 from coyote/accelerate_csv

CYB-332 CSV taking nearly 4.5 minutes to generate
CYB-368 - Gallery: browser back button in item detail view doesn't return to gallery main

https://jira.ets.berkeley.edu/jira/browse/CYB-368
CYB-321 Use Canvas' thumbnailing for non-YT/Vimeo URLs

* Adds a new model, GenericUrl
* Adds queries for #index and #show actions of the GalleryController

https://jira.ets.berkeley.edu/jira/browse/CYB-321
CYB-368 - Gallery: back button - Add JS Docs & resolve comments
CYB-321 - Improved default thumbnail for gallery items without thumbnail
CYB-369 CSV must be required in production environment

* production environment does not include CSV by default
* dropping the draper gem means it was not being included, so
* now it is explicitly included

https://jira.ets.berkeley.edu/jira/browse/CYB-369
Merge branch 'require_csv' of https://github.com/coyote/datacultures into require_csv
CYB-321 - Swapped default thumbnail png for svg
Merge branch 'generic_url_processing' of https://github.com/coyote/datacultures into generic_url_processing
Merge branch 'generic_url_processing' into generic_url_processing_ui

Conflicts:
	app/assets/templates/gallery_list.html
	spec/fixtures/generic_urls/generic_urls.json
CYB-321 Use Canvas' thumbnailing for non-YT/Vimeo URLs

* Adds a new model, GenericUrl
* Adds queries for #index and #show actions of the GalleryController

https://jira.ets.berkeley.edu/jira/browse/CYB-321
Merge branch 'generic_url_processing' of https://github.com/coyote/datacultures into generic_url_processing
Merge branch 'generic_url_processing' into generic_url_processing_ui
CYB-372 Comment activity not showing up in CSV export

* there was a typo in the SQL, so that type of data was not selected
  (It is 'GalleryComment', not 'Comment')

https://jira.ets.berkeley.edu/jira/browse/CYB-372
Merge pull request #227 from coyote/correct_activity_type_typo

CYB-372 Comment activity not showing up in CSV export
CYB-373 Gallery Item duplication
* expired liked items should not show up in the gallery,
   which they do without this code.

https://jira.ets.berkeley.edu/jira/browse/CYB-373