Turn-based Movement, Shooting, Reticle updated

* Basic Turn-based Movement (TBM) implemented between Player and single
enemy (E1)
* Player shooting mechanic updated (was previously a bug that removed
the target and ignored new HP mechanics)
* Reticle remains on targeted enemy even if enemy moves (as long as it
stays within Player's view range)

To Do:
* Implement TBM for multiple enemy units
* Implement enemy units following Player if Player is within sight
* Implement enemy shooting Player if Player is within weapon range