Update console scripts and file-download functionality

Update console scripts and file-download functionality

• Update console scripts (Add more files with sbase mkdir DIR)
• Empty the ./downloaded_files/ folder when a new run begins
  -- (Previously, this happened each time a new browser was launched)
• Add a new method: self.delete_downloaded_file_if_present(file)
• Update the list of SeleniumBase Syntax Formats
  -- (No code changes, but this is a really useful list!)
  -- SeleniumBase/help_docs/syntax_formats.md
• Update several example tests