Added gravity direction to FPC

[luis605]

This pull request adds a gravity feature to the player, enabling the simulation of planetary gravity. The player will now be consistently attracted to a designated gravity point. I implemented this change for my horror game to introduce a 'dream mode,' where gravity can be altered to different directions such as down, left, right, up, diagonal, and more. This modification enhances the player's immersion and overall gameplay experience. Additionally, I have included an 'entities_ignore' list/array in this pull request, which allows raycasts to disregard specific entities.