- fixed background, which was wrong when OptionPane.background is different to Panel.background (e.g. in Hiberbee or Solarized themes)
- use non-UIResource borders in sub-panels to avoid that they are replaced when switching LaF
- added themes list to demo (and testing) apps
- added some popular open-source IntelliJ themes to demo
(downloaded latest .theme.json from source repos;
see themes.properties for source repo URLs)
`JPasswordField`, `JScrollPane` and `JTextField` are non-opaque if they have
an outside focus border (e.g. IntelliJ and Darcula themes).
(issues #20 and #17)
