Allow parallel tests with "-n=NUM" when using "--dashboard" mode, and more.

Allow parallel tests with -n=NUM when using --dashboard mode, and more.

• Add the ability to run parallel tests when using the Dashboard.
  -- (Combine -n=NUM_PROCESSES with --dashboard)
• Change thread-locking of the proxy zip file to process-locking.
• Fix an issue with log files displaying the last browser used.
• Update the check_window() method for visual layout tests.
• Update JS dependencies.
• Update Python dependencies:
  -- filelock==3.0.12
  -- fasteners==0.16

This resolves:

• #870
• #871
• #872
• #873
• #874