Support for system preferences.

New in this release:

• Added set of high contrast themes.
• Added OneDark theme.
• Added option to use system preferences.
• Added option for custom font size.
• Added option for custom accent/selection colors (supported themes only)

• Now all buttons can be navigated using the arrow keys when in a button group.
• Tabs of tabbed pane can now be centerd.
• Tabs of JTabFrame can now be disabled.
• Improved layout for popup menus.
• Added VolumeSlider component.
• Windows now follow the theme background when resizing [windows]
• New improved color picker.
• Combobox popup is now aligned to the border.
• Added icons for image/text mime types (filechooser)
• Added icons for pending/missing html icons.

API changes:

• Renamed shadow variant to borderless (This may break your code)
• The default ToolTipContext can be changed now.
• Added api to LafManager for controlling system preferences.
• Added ThemeSettings as a sample implementation for handling all available options.
• Added function to list all available themes. This can also be obtained as a combobox model.

Addressed issues:

• Focused button could not be activated using ENTER [windows]
• NPE when using tabbed pane in headless mode
• Trees could not be edited.
• Tabbed pane would not respect insets of tab area.
• Radiobuttons/Checkboxes had the wrong background color in SolarizedLight.
• Some icons had some incorrect colors.
• Directory combobox in filechooser would switch directory when navigated.
• Tristate menu item was unusable.
• Removed the gap between a maximized window and the screen edge [windows]
• Fixed content smearing when moving content out of the visible range [windows]
• Incorrect window decoration buttons when creating frame after laf has been installed [windows]
• Java 8 compatibility: removed usage of AWTAccessor
• Some borders and background were not painted consistently. This is no longer the case.
• Some disabled foregrounds were incorrect.