Slowed down the flashing
Revamp of how text is handled

As I went to make the game over screen, I realised the current system made it hard create any new test without it all being attached to the same system, which would get pretty ugly as you try to switch screens. Instead, text is handled through a wrapper to sf::Text, the Text object. I should probably make my own namespace for this stuff, I'll look into it.
Remove the now redundant interface class