Improve functionality of org-passwords.el

Improve functionality of org-passwords.el

* contrib/lisp/org-passwords.el (org-passwords-default-password-size):
  New variable.
(org-passwords-default-random-words-number): New variable.
(org-passwords-copy-username, org-passwords-copy-password): Use
`org-entry-get' to obtain the property value.
(org-passwords-open-url): New function.
(org-passwords): Can be called with universal argument.
(org-passwords-generate-password): Use default size given by
`org-passwords-default-password-size'.
(org-passwords-random-words): Use default number given by
`org-passwords-default-random-words-number'.
(org-passwords-concat-this-with-string): Fix bug.

The patch adds several functionality:

Open the URL property directly from the mode. URLs can be inherit.

Universal argument in org-passwords allows for longer browsing. Two
arguments is used for editing.

There is a default password size and random-words number for faster
password generating.

Fix bug in C-u M-x org-passwords-generate-password.

Commentary in file has more information.