Refactoring the Shell

Created by: stratact

• Remove the evil magic of the static mut raw pointer for Application
• Remove the Application struct all together
• Move Application's fields as variable bindings in fn main()
• Move Application's methods as functions
  • Update the function signatures to mutably borrow the types they used from Application
• Add a &mut Vec<Variable> argument to Command's boxed closure to accept the environment variables lifetimes inside the main field
• Temporarily remove the run command because of bugs.
  • Use exec file:/apps/shell/main.bin <shellprogram> in the meantime.
• Replace all Vec::new() expressions with vec![] macros.