Update license/eula shown in About dialog

Background
When we created a single OSS/Pro binary, we inadvertently dropped all language associated with Nexus Repository OSS being a free product to use. This has caused user confusion and consternation.

Acceptance

• The about box should shows either the OSS or Pro license, depending on whether there is a license installed.
  • "PRO OSS" licensed instances should show the Pro license.
• The OSS license should make it clear that Nexus Repo OSS is licensed under the EPL.
• The 'license installation' dialog should show the Pro license.