Improve JumpAbility

[scastlara]

Jumping feels clunky and unresponsive.

Sometimes you can't jump for some unknown reasons, the difference between a "fast" tap on the jumping button and pressing the key down for some time is too high, making the illusion of "floating" instead of jumping like in Super Mario Bros., the jumping button for Player1 should be "Space" and not "Up", you can get "stuck" on walls...

To fix:

• Why is it unresponsive? JumpKey should always result in a jump. Find the bug and fix it.
• Remap Jump for the two players. Player 1: Space/A button. Player 2: ???/A button.
• Prevent Player from being able to stick to walls. (Is this a JumpAbility problem? or general RigidBody problem?).
• Improve physics to make the jump more "simple", responsive and snappy. A little bit of force added by holding the JumpKey is absolutely necessary, but it shouldn't be as excessive as it is now. Gravity feels low, making the character feel "floaty".

[AdriaPerezCulubret]

Added a gravity amplifier when falling, in order for the jump to feel more responsive and similar to what we're used in videogames. Wasn't able to implement the feature of controlling the amount of jump with the amount of time you press the jump key.

Still have to solve the problem of being unresponsive and the stickiness (which I think they're kind of related).