update /VirtualAppliance page

[graybeal]

Make the following changes to the /virtual_appliance page:

• Change the "documentation" link to point to https://ontoportal.github.io/administration/steps/getting_started/
• Remove the links to the 2.4 Appliance/AMI (actually, put the Appliance link in the section for Administrators, in case we ever need to grab it for some reason)
• Add before the 2.5 Appliance a line that says: "The OntoPortal 2.5 Virtual Appliance is not longer offered for new users. This archival distribution is available only as a backup for those who registered for the Appliance before June 2020."
  • Make the added lines, and the link itself, visible only to people with logins for the page.
• change "Download" header to "Download Latest OntoPortal"
  • Add links to the 3.0.1 appliance and AMI under the Download Latest OntoPortal header
• Create a new header "Archival Links" that goes before the 2.5 content. (The header can be visible. After later releases we will put the 3.0.1 link there, for example).
• Rewrite the top paragraph (currently "The NCBO Virtual Appliance image contains a pre-installed, pre-configured version of commonly-used open source NCBO software running on a Linux operating system. The image was created using VMWare and is available for download at the links below.") for what we're doing now. At least 'OntoPortal'. And do we want to say 'OntoPortal distribution' instead of Virtual Appliance image, and describe the two distribution formats?
• Make the page public

[alexskr]

@graybeal I updated download links and wording. Please take a look. The page requires a valid Bioportal login and the archive section is visible only to registered appliance users.