Add XTerm JS to the server static files

[Ka1wa]

We use Atlantis in an offline environment with the AWS API through PrivateLink. We'd like to use the new real-time logs with XTerm but were having issues because scripts were being loaded through a CDN. We forked the repository and made these changes so we can now use it offline.

Changelog:

• Downloaded all XTerm CSS and JS files and added their respective LICENSES to the source.
  • xterm.css
  • xterm-4.9.0.js
  • xterm-addon-attach-0.6.0.js
  • xterm-addon-fit-0.4.0.js
• Updated all references from CDN to static files in 2 web templates.
• Small fix to make dist. (On my machine it didn't generate bindata_assetfs.go but the default bindata.go. I added the -o option to have less ambiguity)
• Regenerated bindata_assetsfs.go (Seems like this wasn't done in the previous version, there was still a lingering jquery-3.2.1)