- move create_trackbar_setting/update_trackbar_label/create_checkbox from
settings_audio/display/graphics pages to core:settings_common module
- GUI scale trackbar shows the really applied scale, e.g. '3 (effective 2)'
- add gui.get_scale(), gui.get_max_scale(), gui.get_cursor_pos() (UI units);
document that input.get_mouse_pos() returns window pixels
- InventoryView default color is defined once (InventoryView::DEFAULT_COLOR)
instead of duplicated literals; 'color' attribute still overrides it
GUI scale (#737):
- add display.gui-scale setting (0 - auto, 1..4 - fixed integer scale)
- auto mode picks the largest scale keeping at least 640x480 UI units
- apply scale in GUI (root size, camera, cursor, tooltips, scissors)
- HUD layout and ModelViewer use scaled coordinates
- add GUI Scale trackbar to display settings
Volume contrast (#399):
- add audio.volume-contrast setting (100% - unchanged sounds,
0% - loud sounds are lowered to the level of quiet ones)
- loudness (RMS) of a sound is calculated once and cached
- add trackbar to audio settings and reset page
