#914 Ensure current versions are displayed on ESCET website.

• End-user visible changes:
  • The current available release versions are now shown on the ESCET website, in the version selection and on the 'Versions' page, regardless of webserver configuration and browser caching.
• Other changes:
  • Use const instead of var.
• This ensures we can keep announcing milestone/RC releases as soon as their website gets synced to the webserver, rather than having to wait for at least an hour. It also ensures the versions are current for final releases and nightlies.

Addresses #914