Changed, Curve Linedefs mode: re-designed the mode UI. Alternative control...

Changed, Curve Linedefs mode: re-designed the mode UI. Alternative control options are now available (check Help tab while the mode is active).
Changed, Curve Linedefs mode: changed curve generation logic. Setting Distance to 0 will now divide selected linedefs into equal parts.
Changed, Curve Linedefs mode: curve vertices are now drawn.
Updated ZDoom_DECORATE.cfg.