ShaderEditor config file and operator << compatibility

[Csabix]

As of now, if you save the ShaderEditor's contents to a config file (eg.: Shaders/_frag_shaders.config), but if the same shader editor (or the program that the shader editor is a part of) is being populated with shaders using operator <<, then the order in which they appear will be messed up. The errors you get will be non-trivial.

Each time we load a file using the << operator, we should check if that is already in it, and if it is, then move that to the back. (Maybe std::deque<File_t> shaders; in Shaders.h?)

Furthermore, clearing the contents should be an option.
General overhaul of the UI is also needed.