Building towards the first menu

*All the entities now have a second constructor that takes a sprite.
*Entity now has a fade to black function
*Tons of new ids for entities levels and textures and Flags
*Reworked most entity holding vectors to hold pointers to vectors
instead, along with the texturebank. I didn't want to use unmanaged
pointers, but it's the easiest way to go. An extra funcs file has been
added with ways to safely deal with manual memory management.
*Started creating game logic and flag checking, starting with displaying
and fading the splash screen
*Set default textures for things
*Added a couple of placeholder images

TODO: Ensure adding and removal of pointers is correctly implemented and
sanitized within the classes, so that memory deletion only occurs in as
few spots as possible.