Clarify that the optional parameters need to be passed before the command

Syntax: ./dropbox_uploader.sh [optional parameters] <command> ...
Use -B flag instead of --databases
Modify comment border
Remove unnecessary recursive flag from delete statement

Only the -f (force) flag is necessary to force a file to be deleted even if its read only.
Add recursive flag to delete statement of log_backup.sh

The -f (force) flag is necessary to force a file to be deleted even if its read only.
Exit the script immediately if an error occurs