New cost_calculator and ai.find_path_with_avoid() function.

Added new cost_calculator which similar to shortest_path_calculator except new cost_calculator derive terrain_filter. Shortest_path_calculator_with_avoid return getNoPathValue() if dst location match to this terrain_filter.

Added function find_path_with_avoid() for Lua API, that searches for the shortest path and return getNoPathValue() if dst or (intermediate) location equal to locations which setted in [avoid] tag.