Password field instead of ugly hack

This PR fixes the ugly quick-fix my earlier PR made by creating an actual Password field for Nessus, NessusLegacy and OpenVAS scanners. This works for list, create and update scans.

It does this by replacing the \<password\> variable in the parameter string upon submit of the created or updated string. Before displaying it does the reverse, replacing the string with \<password\> and only then shows it on the screen, inserting the actual password in the password field (shows in view-source).

It can display passwords without quotes, but upon saving, it will save all passwords between quotes to allow for complex ones with spaces and non default alphabet characters. I have not tested this with OpenVAS or NessusLegacy since I have neither, but it works fine in the most recent version of Nessus.

This PR also includes some tiny fixes where capitalization wasn't consistent in the scan screens and it fixes issues with the regular expression for extracting a password with complex characters back out of the parameter string.

Please test :)

edit: not sure if the scanners help text needs to be changed..I didn't atm.