+Added definitions for signal signs w2k, w2s, w26a, w26b
*Renamed signal sign w21x to w21_led
*Made w21 sign use a shared rect.svg icon and a static text
+Added rendering of signs attached to signals. If a sign is attached to a signal, attachedAs is set in the sign's def and signal has SignalElements, the sign is no longer rendered on the Signs layer but appears on the signal pole (ifextended signal rendering is enabled)
+Added definitions and icons for signal signs W1 and W18
*Extracted sign attaching logic into attachSign function
+Added signs support in the extended signals parser
+Added signal signs rendering in SignalExtendedRenderer
+Added definitions and icons for W19, W20 and W24 signal signs
*Replaced getPoleLength function of SignalExtendedRenderer with getPolePoints which gives y offsets for all major points of the pole
