[NEXUS-5490] Introduce NexusAuthenticationFilter that delegates AuthenticationToken creation to available AuthenticationTokenFactories

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
[NEXUS-5490] Bind authcBasic/authcNxBasic to NexusAuthenticationFilter that will use factories first to create authentication tokens, falling back to current implement ation from NexusSecureHttpAuthenticationFilter

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge remote-tracking branch 'origin/master' into NEXUS-5490-remote-user
Merge remote-tracking branch 'origin/master' into NEXUS-5490-remote-user
Merge remote-tracking branch 'origin/master' into NEXUS-5490-remote-user
Merge branch 'refs/heads/master' into NEXUS-5490-remote-user
[NEXUS-5490] nexus-rutauth-plugin (add support for REMOTE_USER header)

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
Merge remote-tracking branch 'origin/master' into NEXUS-5490-remote-user
Merge remote-tracking branch 'origin/master' into NEXUS-5490-remote-user
NEXUS-5849: Wrong condition to detect address element

Original code had a bug, an exclamation mark that
negated condition to recognize remote server.

This change fixed that, but also improves code a
bit making it more resilient to empty or null
address tags, and also comparing test against
lowered case.
NEXUS-5690: Javadoced relevant methods, no code change
Merge pull request #112 from sonatype/NEXUS-5490-remote-user

REVIEW: [NEXUS-5490] Extensible authentication token factories & nexus-rutauth-plugin
NEXUS-5849: Using fixed locale for toLowerCase() call
Merge remote-tracking branch 'origin/master' into nexus-5790-new-content-impl