Knockback, stop effects and Skid Trap reworked, monster chase and direction updates, code optimizations
- Created a new function unit_blown_immune that will now serve as the central function to determine if an object can be knocked back or stopped (bugreport:7637)
  * Moved the check code from skill_blown to unit_blown_immune
  * Several stopping effects and traps will now use unit_blown_immune to check if the object can be stopped, if not, the object will always move to its target cell before stopping
  * Bosses and monsters immune to knockback will now no longer be stopped by such traps
  * Expanded the configuration skill_trap_type and moved its checks into unit_blown_immune, so it's possible to switch the "no stop" behavior off for GVG/BG and monsters individually
  * Long-term we should make all skills use this function to check for knockback immunity, it will make the checks a lot cleaner and more centralized
- Monster chase range updates (bugreport:7637)
  * Updated monster_chase_range in monster.conf from 1 to 3; I originally thought official value is 1, but doing some in-depth tests myself I realized it's 3 for the most important situations
  * When a monster cannot issue new "move" commands because it was affected by a status change, but is still moving due to knockback immunity, it will no longer unlock its target and stop
  * Fixed a bug that always caused the chase path monsters calculated to be 1 cell too short causing them to recalculate their path one cell before their goal every single time
- Fixed the direction calculation once again and optimized it at the same time (bugreport:9373)
  * Now the calculated direction is 100% official, really truly, checked it myself with every single cell and various skills
  * Added a new function map_calc_dir_xy that allows to check for a direction between two cells without the need of a block_list
  * map_calc_dir will now just use map_calc_dir_xy to avoid duplicate code
- Implemented Skid Trap properly (bugreport:9373)
  * The direction of the knockback will now be "away from position of the caster during cast" rather than "away from trap"
  * Skid Trap will now stop the target for 3 seconds; this works even in GVG/BG and on bosses, even though the actual knockback doesn't happen