Screenshot previews displayed on dashboard

Updated projects on the dashboard to display preview screenshots when they
have been previewed at least once. There are 3 images of different sizes,
to view each image mouse over the large image. Before a project is previewed it
will display the default origami image.
Updated variable names
Adding route to screenshots
Fixes #496
Merge pull request #497 from adaptlearning/issues/496

Fixes #496
Removed unnecessary variables
Added delete icon to content objects
Added call to read language string
Slight tweak to project tag styling
Added delete icon to course

Also tidied up course tag styling.
Merge pull request #492 from adaptlearning/preview-on-dashboard

Preview on dashboard
Fixes #498
 - uploaded plugins now trigger a grunt rebuild - this will invalidate
   current previews
 - changes to the theme will also invalidate previews, allowing grunt
   to rebuild with the new theme
 - fixed issue where an existing adapt_framework dir would kill install
 - removed grunt build from final install screen - can now log in as
   soon as the app is installed without restarting it
issue #498 - updated screenshot routes
fix for failing tests
Set a background colour for the course previews
Merge pull request #500 from adaptlearning/issues/498

Issues/498
Merge pull request #499 from adaptlearning/delete-icon-standardisation

Delete icon standardisation
Merge branch 'develop' of github.com:adaptlearning/adapt_authoring into slight-screenshot-styling

Conflicts:
	frontend/src/core/project/less/project.less
Merge pull request #501 from adaptlearning/slight-screenshot-styling

Set a background colour for the course previews
Fixes 502