Add to Settings the default folder to be used when downloading attachments

Allowing a user to overide the default folder chosen by Bitwarden would simplify downloading for:

  • users who prefer all downloads - that is, not only those of Bitwarden - to go into a specific folder of their own choosing

  • users who want Bitwarden downloads to go into a specific folder they have created for Bitwarden downloads only

Downloading would be simplified because a user would no longer need to navigate a tree of folders to arrive at the folder they want.