Add a test which boots a computer and runs forever

Ideally we'd add a couple more tests in the future, but this'll do for
now.

The bootstrap class is largely yoinked from CCTweaks-Lua, so is a tad
ugly. It works though.

src/main/java/dan200/computercraft/shared/computer/core/ServerComputer.java

@@ -105,7 +105,7 @@ public class ServerComputer extends ServerTerminal implements IComputer, IComput
     public void update()
     {
         super.update();
-        m_computer.advance();
+        m_computer.tick();
 
         m_changedLastFrame = m_computer.pollAndResetChanged() || m_changed;
         m_changed = false;