Items to fix before next release

[ctrueden]

In the interest of pragmatism, here is a list of issues I want to ensure are fixed before we distribute a new native launcher to all ImageJ users:

• The splash screen might not show up on Ubuntu 18.04. Testing needed.
• Could not find X11 library, not running XInitThreads on Ubuntu 18.04. Track down why.
• ignoring option PermSize=128m; support was removed in 8.0 No reason to keep this flag in the launcher anymore.
• Using incremental CMS is deprecated and will likely be removed in a future release No reason to keep this flag in the launcher anymore.
• Consider reverting Set -Dpython.console.encoding=UTF-8 by default #57 in favor of setting it on the Java side during startup.

CC @LauLauThom @stelfrich