Renaming tests, refactoring tests, adding new unit tests

Made name changes to all files in fixtures, functional, and unit.  I changed all files with "experiments", " experiment", and "experiment_id" to "projects", "project", and "project_id", respectively.

Modified the viz migration file to rename experiment_id with project_id.

Added two functions to test_help.rb for unit tests.  Added assert_default_false to test that a given field is false and assert_default_nil to test that given field is nil.

Refactored all the unit tests for data sets, projects, and users.  Additionally, tested new default fields (filter, like_count, and featured_media_id) in project_test.rb.