Add support for jumping using Space key

Also format the code in Player.cs so that it is more readable.
Add support for left/right keys for movement and up key for jumping
Fix quick direction switching for left/right keys
Fix keypresses not registering when cursor is outside of the game window

Keypresses should be registered regardless of the mouse position. They should only depend on the focus of the window.
Merge pull request #2 from Express50/more-controls

Add support for more controls
Fix bug where PlayerList would not lose focus
Merge pull request #4 from Express50/issue-3

Fix bug where PlayerList would not lose focus
Merge pull request #5 from Cyral/gravity-arrows

Gravity arrows
Improved gravity arrows and input