Updated Updatable::update signature + classes

Removed use of const reference in favor of passing delta time by value.
Added more proxy functions for FileSystem

Trying to reduce usage of PhysFS directly, moving more functionality
into FileSystem.
Implemented sleep/wak for Spawner + ItemSpawner

Spawners need to use the sleep/wake mechanism to spawn items when they
come in screen.
Updated Map interface, name improvement

Changed "get" to "find" since a search is being performed.
Updated gameplay to use waking, no more PhysFS

GamePlayState has been updated to use sleep/wake for item spawners.
Removed direct usage of PhysFS in favor of FileSystem's proxy functions.