#437 Various bugfixes for website version switching

• Best to review per commit.
• Changes:
  • Fix getVersions function in eclipse-escet.js:
    • No more empty items, solving crash on sorting.
    • Prevent empty item in list on versions page.
  • Fix JS import on Chi, CIF and ToolDef pages, for version selection.
  • Include nightly as preview version, also on nightly website.
  • Fix regression in styling of Chi, CIF and ToolDef websites:
    • Accidentally copied over too much when introducing version selection.
    • Also made it consistent now on the about pages.

Addresses #437 (closed)