Consider stronger user token usage promotation with additional properties

[szpak]

Nexus allows to user token's username and password for the promotion-related operations instead of regular username and password. It is somehow safer, as a person having only user token is not able to change the main Nexus password (although it is not possible to limit the scope API access). That feature is almost unknown and although we promote it in README there was an idea by @visi to go a step further and promote them using new credential-related fields.

As a result GNPP would have new properties (something like):

• userTokenUsername
• userTokenPassword

and the corresponding project properties. The old properties would stay as is (should be deprecated one day?), but without promoting them in README or wiki.

Unfortunately, I don't know how to name two parts of the token which is presented in Nexus as:

WDYT?