[tex-live] New installer GUI

[Siep Kroonenberg]

For the 2019 release of TeX Live we intend to provide a new GUI
front-end for the installer. By now, it could benefit from wider
testing.

Just add a parameter '-gui tcl' to install-tl or to
install-tl-windows[.bat] and you shall see the new GUI rather than
one of the old ones.

The Windows .exe installer has gotten a fourth option 'Experimental'
which also invokes the new GUI.

The new GUI uses the Tcl/Tk scripting language.  This is a standard
component of Mac OS. For Windows, a runtime is provided. But
Linux/Unix users may have to install something. e.g., on
Debian-based systems, 'apt install tk' should pull in everything
needed.

Localization: The Dutch localization is mostly complete. For other
languages than English or Dutch, be prepared to see a mixture of
English and native text strings.


-- 
Siep Kroonenberg