Review UI identifier for latest versions

[durack1]

Currently, the ESGF v3.9.5 release uses the identifier "Show All Versions" in the user interface to toggle on or off the "latest" search key.

The default behaviour is for the latest version only to be shown (for a custom URL this would equate to a value of &latest=off - which is not valid search entry), see

https://esgf-node.llnl.gov/search/input4mips/?dataset_version_number=1.1.3&latest=off

Whereas if the search entry the latest value is replaced with &latest=on the search returns a valid search entry, see

https://esgf-node.llnl.gov/search/input4mips/?dataset_version_number=1.1.3&latest=on

In the case of a deprecated dataset

https://esgf-node.llnl.gov/search/input4mips/?dataset_version_number=1.1.0&latest=on

The latest=on means that all versions (even deprecated/hidden data) in this case is shown.

I think this logic should be inverted, so that when latest=on only the latest version (and not deprecated versions) are shown. This would require inverting the logic in the ESGF. Alternatively, the UI text could be changed from "Show All Versions" -> "Latest Version Only", which would then provide a more logical agreement with the &latest=on custom URL

@LucaCinquini @sashakames