Add Linux support

[grillbaer]

• Test on Linux
• Installer from jpackage

[grillbaer]

Debian package build for linux amd64 works, but still needs some refinement: deb package attributes, better target dir instead of /opt to add it to path. Not yet really tested, but at least the windows shows up.

[grillbaer]

• Missing unicode symbols fixed with dependency to ttf-ancient-fonts. Works, but symbols look a little ancient ;-)
• Target dir is now /usr, so Spectracle is in path
• Fixed non-working icon, ok now
• Exposure control flips image to all white when going < 0 ... hm

[telethonic]

Very cool software, many thanks :-)

I tried to create an RPM under Fedora 39 (editing pom.xml to have <type>RPM</type>, and with rpm-build installed), but still getting some errors there.

In the meantime, it runs fine from the JAR files from spectracle-app/target/jmods. I attached the command I used to run it.

As a reference for others, what was installed to enable the build and run:

java-17-openjdk, java-17-openjdk-headless, java-17-openjdk-devel, maven-openjdk17

run_spectracle_command.txt