Issue127 pw

new version of: https://github.com/schubergphilis/Seccubus_v2/pull/127

- This one uses a password field in the database for Nessus, OpenVAS and NessusLegacy scans
- Automatically adds -p for Nessus scans and --pw for NessusLegacy and OpenVAS scans to parameters on the back-end
- Does not load the current password in the edit screen, only updates if new value entered
- defaults.txt and help text changed to reflect the different way of handling passwords.

Open questions: 
- do we need a migration script that handles most of the usecases for migrating from the old parameter style to the new parameter + password style?
- do we need a warning/error when someone DOES enter a -p or --pw in the parameter line?