Map dm_clocktower for HL

DM_CLOCKTOWER - By Victor-933 This is what happens when you combine too much MYST with a taste for the gloomy. Watch your step and be quick on your feet... Texture credits: Poke646, Valve's Deathmatch Classic, Victor-933 (mostly just hacking together existing textures to make ones more suited to the task at hand) Sound Credits: MYST, Gunman Chronicles, Quake 3 Arena