[NEXUS-6373] Remove force base url from general settings ui

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
[NEXUS-6373] Add force base url capability

Signed-off-by: Alin Dreghiciu <adreghiciu@gmail.com>
[NEXUS-6373] JavaDoc
Merge pull request #743 from sonatype/NEXUS-6373-force-base-url

REVIEW: [NEXUS-6373] Use a capability to force base URL