Merge test and tests folder and clean up files

[marthacryan]

• Removes test/vv
• Moves test/percy to tests/percy to consolidate test directories
  • Updates .gitignore and circle CI config to point to new location of percy directory

[emilykl]

@marthacryan IMO -- move the existing tests which were inside tests/ into tests/unit/ so that we have

tests/
  - percy/
  - unit/
    - test_core/ 
    - etc.    

Not strictly necessary because it seems like pytest tests/ "just works" and skips the percy/ dir anyway, but I think it would be ideal to have a directory which contains only the Pytest tests in case we need it.

[emilykl]

🚀