Merge branch 'modularisation'

* modularisation:
  Moving pause message to the hud as that is it's logical location.
  Moving spawn entities into the calculation schedule.
  Moving hud rendering into a module.
  Removing level set, as it's now handled by the setData method.
  Moving data object in player.
  Randomising the spawning of enemy entities.
  Renaming "_populateArena" to "_spawnEntities".
  Removing existing explosions. Explosions will be handled by the entity in future.
  Layering clouds.
  Moving player existance information into player object.
  Adding intro text to the constant arena object.
  Removing a lot of the constant data from main class.
  Removing commented out code.
  Redesigning constants object.