Added variable spawnpoint from map editor

New layer "LevelMetaData" in editor, loads in the old deathzone layer,
as well as a player spawnpoint and any amount of endzone rects. Only
player spawnpoint actually does anything at the mo.
Tweenable Text, Player + Camera end level acting

Tweenables now inherit from the TweenableElement class. Implementing
tweenable sf::text on top of this.
Can get the screenspace offset vector directly from the camera now.
Added some logic to allow locking the player into one input state and
not accept other player inputs.
Game detects collision between player and end of level rect, then locks
the camera and locks the players input state to walk off the screen.
End Level Sequence Working

Time is clickedy clacketed up, and then a grade is given, with sounds.
At the moment the grade is always A+. need to create a config file to
define grade bounds and then hook that up.
Final Changes, Menu Assets In, End Sequence done

This is the build we showed the kids on friday 31st jan, with working
menus and finished ending sequence with proper grading as read from a
config file.