BUG: fix related to saving files in print_pdf method - Issue #20

[joao-voltarelli]

Added changes:

• New key in "prefs" dict in Chrome and Edge, to automatically download pdf files instead of opening a page with pdf viewer.
• Added check_file_count method to count the amount of files of a certain type in a folder.
• Added wait_for_new_pdf method to wait for the pdf file to be saved in the folder, when you don't have the exact file path.
• Added return_last_created_file method to return the last file that was created/downloaded in a folder.
• Changes in the print_pdf method to save the files in the correct path, using the new methods created.

Closes #20

[hhslepicka]

Great work, @joao-voltarelli! Thank you for resolving this bug.