Maestro cannot create encrypted MG_USER_CREDENTIALS resource data

[jng]

Maestro has been creating feature sources with plaintext credentials since the very beginning.

It turns out the secure alternative (with %MG_USERNAME% and %MG_PASSWORD% placeholders) currently is not possible because Maestro does not have the ability to encrypt the entered username/password into the MG_USER_CREDENTIALS resource data.

There is major security implications in not being able to do this as Anonymous users can access such feature source. Denying repository read access breaks rendering/stylization for this user and is not an acceptable workaround.

[jng]

Fixed trunk (r6887) and 4.0.x (r6891)