Disable the OptionsSynchronizer completely

It takes a very long time to synchronize the options wholesale, and while
it was well-intentioned to synchronize the options with the legacy mode
at all, it is highly dubitable that we actually need to finagle the
modern options into the legacy options.

Better to keep them separate, and at the same time save time (also
maintenance time because we no longer have to maintain that beast).

As a bonus, ImageJ2 does not inherit compatibility warts such as the
problematic "black is foreground" setting that cause so many macros to
fail miraculously.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Remove unnecessary parentheses

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make ImageJ2 options non-modal

We are about to add a button to let the user ask to be shown the welcome
message again.

Alas, if the ImageJ2 options dialog is modal, the user cannot even
scroll, let alone put the welcome message into the foreground.

Better to have the options dialog be non-modal; that also lets people
switch off the SCIFIO option just to load a single file that SCIFIO might
not be able to load yet and immediately switch SCIFIO back on.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a button to the ImageJ2 option dialog to display the welcome message

Some users have missed the message because this developer forgot to
upload the WELCOME.md file. D'oh.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
'What is ImageJ2?': fall back to other means to display the message

We have so many services to fall back on...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>