Implement in Jalview (and getdown for JVL) the use of specific scheme names for different channels (e.g. jalviewd://)

Since the first install4j installers, a proper desktop installation of jalview registers a URL scheme/protocol to open a URL with Jalview, e.g.

jalview://www.jalview.org/examples/uniref50.fa

will open Jalview and pass it the URL "http://www.jalview.org/examples/uniref50.fa" causing Jalview to download and open that file.
Similarly, "jalviews://..." will open "https://..."

There are two stages to this:
1) install4j has registered these schemes with the user's OS configuration so that when a user uses one of these schemes the OS knows to open Jalview.
2) getdown then intercepts the scheme name and changes it to "http" or "https" before adding it as an argument for launching Jalview proper.

The jalview and jalviews schemes are fully implemented and work.

For Jalview Test and Jalview Develop, these schemes are also registered, along with an extra scheme "jalviewt" for Jalview Test and "jalviewd" for Jalview Develop. The intention for these was so we could "force" (or at least strongly suggest to the OS) that the URL should be opened in one of these installations specifically.
[ as an aside, note that switching a release installation to the test channel will not add this scheme, since the registration is performed by the Jalview Test install4j installation ]
[ as another aside, if the host part of the URI is empty, then only the PATH part of the URL is used and passed on its own, so it opens as a local file ]

However, getdown ignores these extra schemes and Jalview opens without an additional argument.

This has not been an advertised feature and it is unlikely anyone is using it -- the intention was that we might be able to leverage it for specific JVL files that we want someone to test.

To fix:
- https should now be assumed.
- "jalviewhttp" and "jalviewhttps" should also be registered in install4j (only affects new installations).
- Getdown should deal with any "jalview" or "jalviewX" schemed URIs being passed as first argument (it is install4j that registers specific schemes to different installations).
- Getdown should deal with "jalviewhttp" and "jalviewhttps" schemes.