Projects should be searchable

In /views/course_editions/projects/index, there should be a search function.

• /views/course_editions/themes/index already has a search function, and many of the logic could be copied from there.
• Model project should include elasticsearchable
• Model project should include settings do block (see models/theme for example) which describes to elasticsearch which information should be indexed.
• controllers/course_editions/projects_controller should also have filter actions (see controllers/course_editions/themes_controller for example)