Fix armor groups spawning bugs

* Prevent common cases where ground units do not spawn due to
  frontline position being in exclusion zone

* Fix case where ground units will spawn inside exclusion zone due to
  random offset from frontline center being fixed

* Remove dead code from `conflictgen.py`

* Start cleanup of `GroundConflictGenerator`

game/utils.py

@@ -42,4 +42,16 @@ def mps_to_knots(value_in_mps: float) -> int:
 
     :arg value_in_mps Meters Per Second
     """
-    return int(value_in_mps * 1.943)
+    return int(value_in_mps * 1.943)
+
+def heading_sum(h, a) -> int:
+    h += a
+    if h > 360:
+        return h - 360
+    elif h < 0:
+        return 360 + h
+    else:
+        return h
+
+def opposite_heading(h):
+    return h+180