Linedef Color Presets: completely redone Linedef Color Presets UI. Now it's...

Linedef Color Presets: completely redone Linedef Color Presets UI. Now it's done the same way as Things Filters UI.
Linedef Color Presets: Linedef Color Presets can now be disabled.
Things Filters window: a warning icon is now displayed near the filter name in the filters list when the filter has no usable settings.
Change Map in Current WAD window: keyboard focus was not set to initially selected item.
Changed the default wad filename from "unnamed.wad" to "[map name].wad".
Updated documentation ("Custom linedef colors" page).